What a great thread! I just lurk since I sold my NSX a few years ago (it's in Hawaii now, lucky car) but had to add a comment.
My experience with modding has finally given me this perspective: Fantasy vs Reality. Most mods can be viewed this way: the fantasy of the improvement the mod is supposed to make, how good it will feel, how great it will make your car; the reality of how little difference the mod really makes, its sub-OEM quality, its poor fitment and the comprises you must suffer with due to its installation.
To each his own but to me the vanity mods -- which for some reason are supposed to look mean or cool -- are the worst. People do these things to their cars that absolutely destroy their driveability... but it looks cool. I guess that's fine if one is all about looks and not substance. The other is trying to make a track car out of a car that spends 99% of its life on the street. If those mods actually work, well, then at least it's substance. If the owners wish to live with the street compromises, they're entitled, but I don't get it.
My bottom line, especially on a high-end performance car, is they are carefully engineered by people who know what they are doing to achieve a certain balance -- with much more development dollars than any aftermarket maker can afford. I'm not going to spoil my car and waste a lot of money. I now enjoy my cars for what they are and appreciate a pristine stock example more than any other. If I think I want to make a mod I see it and feel it on someone else's car first to see how close the reality is to the fantasy. Most of the time, it's not even close.