I'd like to see the car choices revamped.
For example, there are like 7 Miatae in the game, yet in real life, there are really only two, but with different option packages. The Sunburst Yellow limited edition car is no different than any other Miata of the same year, except the color. Ditto with the M Editions, except they add some more luxury features. I see no R package or sport package cars, either, but again, they are merely an option for the car, not a special edition.
So what should happen is you go to the new car shop and choose a Miata. Now you choose your generation (89-93, 94-97, and 99 and up) then you choose your option package, which determines which engine you get (in the US, there is no option, different years had different engines) whether or not you get a limited slip stock, and whether or not you get the sport suspension and brakes.
Skylines are another example. How many R34s does there really need to be? One for the street, really. GTR, GTS, V Spec, VSpec II, its all just different options for the same car.
Eliminate the redundancy so that more unique cars can be included.