I agree, we do need our own tracks, especially some rally ones so we can try out those game modes... but no one has stepped up, yet. :-) Part of the problem is probably the non-trivial track creation process, but really, the hardest part is just modeling the track in blender. I could take care of the rest if someone else models something in blender.
kcid, I can't wait to see your tracks. In fact I might be able to contribute a little to them, if you check them into the art repository. I could do track objects, or parts of the road themselves if you like.