I like this approach, easy for people to add to it. I have a database of about 380 tracks right now. Some cleanup needed but the core information is there. It leverages google maps api too: http://www.kartpulse.com/TrackListings/map
I worked with a few different sources including Richard Thoms from racingwhere and a guy called BT Owens who had a similar map to yours for some dirt tracks.