Yaw!
Excellent idea.
We toyed around with the idea of adding potholes, never did though.
We were also thinking of making the driving area look more like road. Bare driving surface in the lanes (where cars contact the track most often), then on the outsides, near the where the 'shoulder' would be, adding fine grit sand or sandpaper. Just enought to allow a little slip and slow, but not crash. Like on 'touring' tracks IRL.
I also have another idea for 'short-cuts'. Just like in games, the short-cut would be extremely hard and daunting, not inviting at all, so most would prefer the normal route. However, if there happens to be some egocentric driver that thinks he can do it all, he has the opportunity to take the short-cut. But, he had better be as good as he thinks, because 1 mistake means the short-cut turns into the longest section of track in your life.
And yet another idea is to create 'scenes'. Like driving on a normal track, then suddenly there's a clear, round, plastic tube, leading off the track - through an aquarium - and back out the other side!
I think that would be awesome. If you did it right, the tube would be just slightly larger than your bit, and it's round, so theoretically, as long as you were lined up correctly for the entrance, you could floor it in the tube, not have to worry about steering as the tube would force the car into the path of least resistance, which would be straight on down the tube!

Okay, back to reality.