Having been following these threads, I'm just going to observe here that it's possible, as I do, to acknowledge that the show could have done more to develop Nia, but still love what is done with her.

I have issues with the way Gurren Lagann handles its female characters (yes, Yoko too). I essentially agree with everything csakuras and 7thisgod are saying about Nia's development--I think it was there if you look hard enough--but I am disappointed that so much of it was subtext, whereas so much of a lot of the rest of the cast's development was text. I understand why other people would find her less interesting than some characters, but I don't think she's less complex...just somewhat mishandled. I hold out hope that the second movie will give Nia some actual action and screentime towards the end, so we can see her own thoughts and decisions instead of having to guess at them, but that won't fix the flaws of the original show.

Also, while Simon/Nia may be too "perfect" for your tastes, I like it a lot because I feel like it justifies its perfection (as well as appealing to my fondness for certain types of connections between characters). We're not told "Simon and Nia are ridiculously good for each other," we're shown it. You may prefer more conflict in your pairings (and I usually do too), but Simon/Nia appeals to the part of me that likes really big, epic love that's also just plain cute.