I have to say, this mod is great, nice work! I've been enjoying it quite a lot.
My biggest nitpick would be the lower quality sounds on some cars, but that is not so easy to change.
What I would like to see tweaked however, is physics on some cars. Most of them feel really good even with keyboard, but there are some that have annoying stability problems on imperfect roads. So far the worst has been the upgraded Lotus Exige S. Zero throttle, just rolling in a straight line, road goes up or down a bit, car slides out and crashes into a tree on its own. I don't know how the game handles suspension and the like, but it feels like the car is too stiff for such low poly roads.
Edit: Oh yeah, one more imperfection I noticed is car groups, some of them are too high or low. I have one example for this, the Audi RS4. I think it should be grouped to D and not E.