I quit gagging at the bodykit idea and the option of the garish paint jobs, since it exists in real life. I can see that a quarter of the kids will be ricing their cars all to hell, but then online, we'll know who the twerps are.
And I don't mean things like make/sports accessory decals and the like. I like Putti's idea, and the ones in this thread.
Taking off on an idea from someone who mentioned this in a previous thread, I'd like to see the dealer car list simplified, but also expanded on. Like, say you're going to get a Subaru WRX. Rather than have three or four of the different versions in a long string of cars, there's ONE car in the list. Select that, and the different models drop down like the STi's, and you can select different options like tails, sports packages, as well as paint job. EDIT: And yes, this means 50 Skylines, so deal with it.
I like the idea of having sport level upgrades available at the dealer, especially at a discount, but that's just a suggestion. It does go with the idea given in this thread, and it gives you a greater sense that you're buying and owning a car, your car.
I also like the idea of having a few years worth of high quality used cars available, as much as four or five years old. They could be the best quality of the used cars. Then the used lots would have all the rest. And like I suggested before, you should find used cars that are riced up or modded already, and special cars that show up rarely. That would give you a few mods at a discount - higher price than a stock used car of course, but cheaper than adding the mods yourself.