Each person has their own individual taste, I like standard cars or some body kits aslong as they are understated and aid the looks of the car, I myself like the smooth look, so no spoilers, bump strips, decals. I like the car to look clean instead of placing a vent in to any panel with a space larger than 3cm on it.
If people want something different than me then fine, I would prefer it if they let people customize as much as possible, that way you can judge what is coming and either die of laughing, take a different route to avoid a crash or agree that you like their style too depending on how many pieces of barbies summer cottage are stuck to it.
I am presuming that the customisation will amount to the same as Forza3's, so ill be stuck with changing rims and paint, but that's perfectly fine to me. - I hope they'll let you remove the registration plates on the car so you can create your own through decals like i had to on forza3.
But, even if we can only modify paint... there are always people who will do this: