The appearance could be more than purely cosmetic and it can be applied in many flexible ways. Imagine that during character creation, if you choose a different height you’ll need to fix it by two menus, one of advantages that you will need to rebalance by another of disadvantages (I don’t know the real game variables so I’ll be guessing the examples).
Advantages menu for taller heights: +1 Strength, +1 Resistance, +3 Intimidation, etc...
Penalties menu for taller heights: -1 Dexterity, -3 Reflex, -3 Stealth bonus, etc...
So, if you want to be taller, you will need to configure your own advantages/disadvantages from menus that contains only the stats that are affected by body size (ie you won’t see Wisdom in Height menus). Here are a few examples of possible final configurations:
1st possible configuration for a tall person: +1 Strength /–1 Dexterity
2nd possible configuration for a tall person: +3 Intimidation /-3 Reflex
3rd possible configuration for a tall person: +1 Strength +1 Resistance /-6 Stealth bonus
By this way you will have a unique character far from the basic stats. In the same way, when you see a tall NPC in the game, you won’t know if he will be strong or only intimidating. This system could be applied in more ranges by multiplying the basic points of advantages/penalties in some way like this:
Smallest (+2/-2), Small (+1/-1), Average (+0/-0), Tall(+1/-1), Tallest(+2/-2).
Also could be applied to all aesthetics even in asymmetrical ways. The following examples are for beauty:
Ugly: x2/x2 to all Unsightly choses
Unsightly: +3 Stealth /-1 Seduction (you are less noticeable by others)
Normal: Average
Beautiful: -6 Stealth -3 Speech/+2 Seduction +1 Luck (you are noticeable and don’t need to talk often)
Gorgeous: x2/x2 to all Beautiful choses
This can go even more deeper, for example, a beautiful person who wears a helmet can easily lose all benefits (Seduction) but continues carrying some penalties (Speech) while others may be gone (Stealth).
The possibilities are endless and pretty easy to implement to the character creation stage. You better think about it.