I agree on the Red Bull GRC style but tweak it down a bit to be more viable for finding wheels, suspension, etc that are more street/track oriented, perhaps an easy to swap smaller and larger spliter, two wings, one more aggressive than the other but both real wings, functional under tray but also still street friendly.
Added:
One thing I really like on the GRC cars is the back of the fenders are open with mud flaps over them as easily they can serve several purposes.
Flaps off, road racing, autocross, or even a quick canyon run, it allows a lot of air to escape from the area as well as some from under the car.
Flaps on, winter driving, rally cross, even street if you just like the style but still functional.