Quoted from metallik:IMHO, mods usually zero out... they don't add much value, but as long as they're easily removable, they don't detract either.
Some mods increase value, a few significantly increase it (Tron ramp lights, Medisinyl RZ spine, among others)
I'm right there with you:
A few (very few...) Mods add a good value
Most add little to no value
A few actually lower the price (especially if they can't be easily removed)