In general, is it better to (a) have every character specialise in a particular area e.g. Aloth specialises in History, Xoti in rekigion, or (b) spread the points around so everyone gets a bit of everything.

Assuming you are talking about conversation checks, in general it's way more beneficial to spread points evenly, at least in passive skills.

In conversations, the Player gets an assist bonus (most of the time) to their skills based on total points of the rest of the party:

    Crew Total  Bonus
    1...........1
    2...........2
    4...........3
    7...........4
    11..........5
    16..........6
    22..........7
    29..........8

For example, if Player has 4 Bluff, and the rest of your crew has total of 12 Bluff, the total score is 4 + 5 = 9.
So it doesn't matter if a party member has exceptionally high points in one skill, only the average matters.
And as you can see from the table, you get diminishing returns at high skill levels, so "specializing" a party member in a certain skill for a high total is suboptimal. If you try to even out the total by giving everyone else low points, you'll find the skill dropping radically whenever you remove your specialized member from the party, which is a massive inconvenience.

There are a few exceptions to this rule, however.
The abovementioned formula is also used for calculating lockpicking difficulty with Mechanics, so you get much more benefit from a single character with a lot of points in Mechanics.

Scenario 1: Aloth has 11 Points in Mechanics, everyone else has 1 each (total 4). Lockpicking Level: 11 + 3 = 14
Scenario 2: Aloth has 3 Points in Mechanics, everyone else also has 3 each (total 12). Lockpicking Level: 3 + 5 = 8.
Both parties spent 15 points in Mechanics, but the first is significantly better at lockpicking.

There are far fewer Active skill checks than Passive ones, so it's not crucial to put points into those just for story purposes.

There are also checks in scripted interactions where you select which party member should attempt the check. It'll still be assisted, but in these cases you benefit if that character's own skills are high. A lot of these checks are Athletics and Survival, so it might be worth giving someone a few extra points in Survival.

There are a couple items that increase in potency based on specific skills, such as Xoti's weapons. Depending on how high you prioritize min-maxing and passing conversation checks, you might want to put extra points in skills for characters that use those items.  However, it's worth mentioning that not all of these items have very noticable scaling.

Total number of checks per Skill:

Spoiler

Player Solo

Alchemy: 2
Arcana: 2
Athletics: 27
Bluff: 9
Diplomacy: 5
History: 5
Insight: 29
Intimidate: 7
Mechanics: 1
Metaphysics: 17
Religion: 14
Sleight Of Hand: 10
Stealth: 2
Streetwise: 8
Survival: 12

::::::::::::::::::::::::::::::::::

Player Assisted

Alchemy: 17
Arcana: 38
Athletics: 35
Bluff: 166
Diplomacy: 178
Explosives: 7
History: 77
Insight: 188
Intimidate: 157
Mechanics: 12
Metaphysics: 58
Religion: 50
Sleight Of Hand: 33
Stealth: 7
Streetwise: 95
Survival: 35

::::::::::::::::::::::::::::::::::

Selected Solo

Arcana: 1
Athletics: 35
Bluff: 1
Explosives: 2
History: 1
Mechanics: 4
Religion: 2
Sleight Of Hand: 8
Stealth: 3
Survival: 4

::::::::::::::::::::::::::::::::::

Selected Assisted

Alchemy: 12
Arcana: 8
Athletics: 48
Bluff: 9
Diplomacy: 3
Explosives: 10
History: 11
Insight: 9
Intimidate: 5
Mechanics: 24
Metaphysics: 2
Religion: 22
Sleight Of Hand: 10
Stealth: 49
Streetwise: 9
Survival: 57

::::::::::::::::::::::::::::::::::

 

 

Edited March 19, 20205 yr by Noqn

Unassisted Player checks (no bonus from crew):

Spoiler

Total count:

Alchemy: 2
Arcana: 2
Athletics: 27
Bluff: 9
Diplomacy: 5
History: 5
Insight: 29
Intimidate: 7
Mechanics: 1
Metaphysics: 17
Religion: 14
Sleight Of Hand: 10
Stealth: 2
Streetwise: 8
Survival: 12

__________________________________________

Skill Requirement / Count

Alchemy
        6       2

Arcana
        10      1
        13      1

Athletics
        1       3
        2       2
        3       6
        4       3
        5       4
        6       3
        7       2
        8       1
        11      2
        15      1

Bluff
        3       1
        6       2
        8       2
        9       1
        12      1
        13      2

Diplomacy
        1       1
        4       1
        5       1
        10      1
        16      1

History
        1       1
        2       1
        4       1
        6       1
        7       1

Insight
        2       5
        3       4
        4       5
        5       4
        6       4
        7       2
        8       4
        10      1

Intimidate
        3       1
        4       1
        5       1
        7       2
        10      1
        12      1

Mechanics
        5       1

Metaphysics
        3       1
        4       2
        5       6
        6       3
        8       5

Religion
        2       1
        4       2
        5       4
        6       3
        7       1
        10      1
        12      2

Sleight Of Hand
        3       1
        4       1
        5       3
        6       2
        8       2
        10      1

Stealth
        2       1
        4       1

Streetwise
        2       2
        4       1
        6       1
        7       1
        8       1
        10      1
        12      1

Survival
        1       2
        3       2
        4       3
        6       2
        8       2
        9       1

Assisted Player checks (with bonus from crew):

Spoiler

Total count:

Alchemy: 17
Arcana: 38
Athletics: 35
Bluff: 166
Diplomacy: 178
Explosives: 7
History: 77
Insight: 188
Intimidate: 157
Mechanics: 12
Metaphysics: 58
Religion: 50
Sleight Of Hand: 33
Stealth: 7
Streetwise: 95
Survival: 35

__________________________________________

Skill Requirement / Count

Alchemy
        2       1
        3       2
        4       4
        6       4
        10      3
        11      1
        15      2

Arcana
        1       1
        2       5
        3       1
        4       5
        5       2
        6       3
        7       1
        8       1
        12      1
        13      2
        14      3
        15      4
        16      1
        17      3
        18      4
        19      1

Athletics
        2       7
        3       4
        4       4
        5       4
        6       2
        7       1
        8       1
        10      2
        11      1
        12      8
        15      1

Bluff
        1       2
        2       17
        3       19
        4       18
        5       7
        6       13
        7       13
        8       15
        9       4
        10      14
        11      5
        12      6
        13      4
        14      8
        15      12
        16      3
        17      2
        18      1
        19      1
        20      2

Diplomacy
        1       2
        2       20
        3       14
        4       29
        5       17
        6       16
        7       10
        8       21
        9       5
        10      12
        11      2
        12      8
        13      5
        14      5
        15      1
        16      4
        17      5
        20      1
        23      1

Explosives
        4       1
        5       1
        9       1
        10      2
        16      1
        17      1

History
        1       2
        2       11
        3       8
        4       12
        5       10
        6       7
        7       8
        8       2
        9       3
        10      2
        12      2
        13      2
        14      2
        15      3
        17      1
        18      2

Insight
        1       6
        2       24
        3       37
        4       28
        5       11
        6       15
        7       6
        8       12
        9       3
        10      16
        11      4
        12      4
        13      2
        14      6
        15      7
        16      1
        17      2
        18      3
        20      1

Intimidate
        1       4
        2       15
        3       15
        4       23
        5       12
        6       10
        7       8
        8       20
        9       10
        10      10
        11      1
        12      5
        13      3
        14      2
        15      2
        16      8
        17      4
        18      4
        22      1

Mechanics
        1       1
        3       4
        4       1
        8       1
        9       1
        10      1
        12      3

Metaphysics
        2       5
        3       3
        4       5
        5       8
        6       6
        7       1
        8       2
        9       3
        10      6
        11      3
        12      2
        14      1
        15      9
        17      1
        18      1
        19      1
        20      1

Religion
        1       1
        2       3
        3       4
        4       2
        5       6
        6       1
        7       6
        8       4
        9       4
        10      4
        11      1
        12      7
        13      3
        14      1
        15      2
        16      1

Sleight Of Hand
        2       7
        3       7
        4       4
        5       5
        6       1
        7       3
        8       1
        12      1
        15      4

Stealth
        2       1
        3       3
        4       2
        10      1

Streetwise
        1       3
        2       12
        3       16
        4       16
        5       11
        6       12
        7       5
        8       4
        9       3
        10      1
        11      1
        12      1
        13      4
        14      2
        15      3
        20      1

Survival
        2       1
        3       3
        4       11
        5       5
        6       3
        7       1
        8       3
        12      2
        13      1
        14      3
        15      1
        18      1

Unassisted Selectable member checks (no crew bonus):

Spoiler

Total count:

Arcana: 1
Athletics: 35
Bluff: 1
Explosives: 2
History: 1
Mechanics: 4
Religion: 2
Sleight Of Hand: 8
Stealth: 3
Survival: 4

__________________________________________

Skill Requirement / Count

Arcana
        4       1

Athletics
        1       1
        2       3
        3       6
        4       5
        5       4
        6       5
        7       1
        8       5
        9       1
        11      3
        15      1

Bluff
        8       1

Explosives
        12      2

History
        1       1

Mechanics
        5       2
        11      2

Religion
        5       2

Sleight Of Hand
        5       2
        6       1
        9       2
        10      3

Stealth
        10      2
        13      1

Survival
        4       3
        9       1

Assisted Selected member checks (with crew bonus):

Spoiler

Total count

Alchemy: 12
Arcana: 8
Athletics: 48
Bluff: 9
Diplomacy: 3
Explosives: 10
History: 11
Insight: 9
Intimidate: 5
Mechanics: 24
Metaphysics: 2
Religion: 22
Sleight Of Hand: 10
Stealth: 49
Streetwise: 9
Survival: 57

__________________________________________

Skill Requirement / Count

Alchemy
        7       2
        12      1
        13      1
        14      2
        16      4
        17      2

Arcana
        8       1
        12      4
        14      1
        15      1
        20      1

Athletics
        3       3
        4       3
        5       2
        6       2
        7       3
        8       6
        9       2
        10      10
        11      2
        12      4
        13      2
        14      1
        15      1
        16      2
        18      2
        19      1
        22      2

Bluff
        7       1
        10      2
        12      4
        13      1
        15      1

Diplomacy
        7       1
        14      2

Explosives
        9       5
        10      2
        14      2
        20      1

History
        1       1
        10      3
        12      1
        13      4
        14      2

Insight
        1       2
        8       2
        12      2
        13      1
        15      2

Intimidate
        7       1
        8       1
        13      1
        16      2

Mechanics
        2       2
        5       1
        6       1
        8       3
        9       1
        10      4
        11      1
        12      2
        13      1
        14      3
        15      2
        17      1
        26      2

Metaphysics
        5       2

Religion
        3       1
        5       4
        6       2
        7       5
        8       1
        10      2
        11      2
        12      1
        15      4

Sleight Of Hand
        2       3
        3       1
        9       2
        13      2
        15      1
        18      1

Stealth
        1       1
        2       2
        3       3
        4       3
        5       3
        6       2
        7       4
        8       6
        9       2
        10      7
        11      1
        12      4
        13      3
        14      4
        15      1
        16      2
        18      1

Streetwise
        3       1
        5       1
        7       2
        8       1
        10      2
        15      2

Survival
        1       2
        2       3
        3       1
        4       3
        5       2
        6       5
        7       3
        8       6
        10      6
        11      2
        12      4
        13      6
        14      2
        15      6
        17      4
        19      2

 

Edited March 19, 20205 yr by Noqn

Thank you. Would you mind explaining the tables that you put in the spoiler tags?

9 hours ago, Noqn said:

Assuming you are talking about conversation checks, in general it's way more beneficial to spread points evenly, at least in passive skills.

 

9 hours ago, Noqn said:

And as you can see from the table, you get diminishing returns at high skill levels, so "specializing" a party member in a certain skill for a high total is suboptimal. If you try to even out the total by giving everyone else low points, you'll find the skill dropping radically whenever you remove your specialized member from the party, which is a massive inconvenience.

 

This is not quite correct.

In many skill checks, you can choose which party member to use, at which point you're not talking about diminishing returns; every point you put in a skill is a full point you get in that skill. Instead of having e.g. four supplemental party members that each put bluff 4, you're better off having one party member have 16 bluff, and the other three party members specializing in another skill each. In terms of bonus points to the watcher or other party members, the math is still the same, except now you have enough skill points in a single party member to pass a difficult check if needed.

Though the hardest skill checks appear to be watcher-only.

 

Edited March 19, 20205 yr by thelee

3 hours ago, thelee said:

This is not quite correct.

In many skill checks, you can choose which party member to use, at which point you're not talking about diminishing returns; every point you put in a skill is a full point you get in that skill.

I know, I wrote that in my post:

12 hours ago, Noqn said:

There are a few exceptions to this rule, however.
[...]
There are also checks in scripted interactions where you select which party member should attempt the check. It'll still be assisted, but in these cases you benefit if that character's own skills are high. A lot of these checks are Athletics and Survival, so it might be worth giving someone a few extra points in Survival.

___

3 hours ago, thelee said:

Instead of having e.g. four supplemental party members that each put bluff 4, you're better off having one party member have 16 bluff, and the other three party members specializing in another skill each.

In which case the remaining five Passive skills will be at 0 points each. 
You'll also find that benching that particular character drops your Bluff bonus to zero, which doesn't exactly make for flexible party management.

Just so that we are clear about the frequency of selectable checks and to put things into perspective, here are the total number of (passive) Player checks w/assist and total number of crew checks:

Player w/assist
Bluff: 166
Diplomacy: 178
History: 77
Insight: 188
Intimidate: 157
Metaphysics: 58
Religion: 50
Streetwise: 95
Survival: 35

Crew w/ assist (+ Crew w/o assist)
Bluff: 9 (+ 1)
Diplomacy: 3
History: 11 (+ 1)
Insight: 9
Intimidate: 5
Metaphysics: 2
Religion: 22 (+ 2)
Streetwise: 9
Survival: 57 (+ 4)

Notice how there are only 10 selectable Bluff checks in the entire game? Besides Survival and to a lesser extent Religion (which together cover 63% of all selectable checks), there's practically zero reason to specialize in passive skills. Most of these can be passed with evenly distributed points anyway, such as the two Metaphysics checks, both at 5.

Even if you go for the more optimized approach of spreading the character across two skills each (and "only" sacrificing one passive skill), the party management issues still remain. If are talking about a custom party, that's obviously not an issue, but I presume that's not what OP was asking for.

Edited March 19, 20205 yr by Noqn

8 hours ago, Hayashi.226 said:

Thank you. Would you mind explaining the tables that you put in the spoiler tags?

Sorry. It's the number of skill checks throughout the game, sorted by requirement and grouped by whether it's for the Player or a selectable party member, and whether you get a bonus from the rest of the party or not. Just fun statistics.

Edited March 19, 20205 yr by Noqn