I kinda agree with BM. Having always gone for the best bits I can get I get the fit, finish and residuals I want. I can also understand why people buy copies - the world has it with everything. Clothes, electronics, films, car parts and so on. Fact is those people are ultimately cutting their nose off to spite their face.....
I bought a bunch of Alpine and JL Audio stereo equipment a few years ago. Even today it still works like new, wins prizes at shows and is worth good money second hand. If it was Sony xPlop or whatever, it's be worthless. But most importantly IMO - it is BETTER than what was there before. The main thing I don't understand is people taking a £30k sportscar that had years of development to get it to handle and feel the way it does, and then people put wheels that weigh twice as much on or lower it with a few hundred quid. What makes you think someone who has never driven the car in anger can make it better with a quick fix?!
Modifying is a bit more subjective and style (or lack of! ) comes into it. Some bits are actually overpriced so if someone can make something better for less, then great. However, in a supply and demand market, that doesn't tend to be the case. I have yet to see a NISMO replica kit that can't be spotted immediately in the flesh for example (as different from a genuine one). That doesn't mean the replica looks bad, but you can tell.
So I would look for whatever it is to have substance as well as form at the minimum........