Firstly I have to say I've only played NWN2 of your games, and for me the two most interesting characters were not romance options - Neeshka, and Khelgar. My male tiefling would love a bit of tail, and my female dwarf loves the battle crazed Khelgar (ok so she is a Priest of Clangedin).
The thing you skipped that was the problem in the romance for me is personality and conversation.
Casavir had basically no conversation and thus really developed no personality beyound "dour".
Elanee just annoyed the heck out of me with her self rightousness. The Druid was more judgemental than the Paladin, and she turns out to be a psycho stalker woman, breaking suspension of disbeleif if you are not playing a short lived race ie human.
This is compounded by the fact that, at least in Casavir's case (I have not stomached Elanee that much yet), he finally confesses his love, you hop in the sack and then you cannot talk to him about it again. Same old redundant conversations as before... aaarrgghhhh. More than anything that ruined the Casavir romance, the fact that there is no way for your character to express an interest in him before his confession just makes it worse. At least with Elanee there is a chance to make suggestive comments earlier in the mod (you can ask if she is offering to have your kids, which she, showing an utter lack of wit, rejects).
I know that creating romance is hard going, but romance is far more meaningful when you can communicate with the intended person, and the intended person communicates back. Interaction when the PC is not around is meaningless, its "Out of Character' information. What matters is what the NPC does when the PC can see it, and what the NPC does with/for/to the PC. Just hanging out and killing monsters is a foundation for friendship, it takes a lot more to get some love happening.
Oh you also might want to try following this thread and its 2 subsequent Romance threads (yes over 30 pages of discussion) to get some ideas of what a bunch of players think about romance. (Plus some interesting debate about Romance, Love and Alignment.)