Looks very interesting. I have a few ideas if you didn't have them already which I'm sure you did. Maybe some snow overlapping the edges of the track. Unless the trees are evergreens maybe have the without leaves.
Since it's an experiment, there's something you can try : snow real road (although it's probably not wanted for a race on a permanent track...) Try to put a snow texture as your diffuse road texture, and your road texture replaces the racegroove one. The racegroove texture is multiplied with the diffuse, and since the main texture is white, the asphalt should appear on the racing line.
