I'm not a big gearhead, I'm not really into racing cars myself, heck I rarely watch racing at all. Yet, Gran Turismo is my favourite video game series. Basically, I'm just a geeky gamer that relies on twitch skills to be good at GT, rather than a deep knowledge of the strategies etc. involved in actual racing.
Now that I've run my reputation into the ground, I can freely say that I see absolutely nothing wrong with cosmetic body kits. Heck I would even be happy to see all kinds of decals and things to plaster on my car. Customizing the appearance of your vehicle is something that I think is pretty cool. (and don't say "Go play NFS:U" cuz I have played it, and I don't like how it handles. Also, it has less than 1/10th of the cars in GT 4, and you never really feel like you own any of them) It's especially cool because of online racing, where it would certainly add to the satisfaction of victory if you beat the guy in a ride that had it's own unique appearance.
Apart from being a complete waste of money, I see nothing wrong with ricers in general actually.