Seriously, in my opinion there's not really any need to ask any questions here unless you want to break new ground, everything game related is right here in the forums.
On that note I should probably give credit to all the people posting tutorials and solutions here. CHEERS!
Man. I wish we had more people like you around here. You are a legend!
Just one question: Have you had previous experience with making stuff for games? You seem very talented at it.
Some more comments about the tracks:
If you are not going to remove the enduro fences, you should at least make it a little bit wider. There is 0 room for error at the moment.
Traction: I had a look at the values that you used. I found it odd that you decreased friction as wheel-slip increased. This does make sense for hard pack (particularly wetted hardpack) when you think about it. But for the enduro, where the mud is more "thick", I think the friction should increase, as well as increased resistance. When the tyre can sink into the dirt, the friction will increase due to the buildup of dirt when it is slipping. That is why ABS brakes are not as good on dirt. Maybe have it slipperier in the rocky sections though, as they will naturally be more slippery with wheel-slip. Something definitely needs to be done about the slipperiness in the gutters on the side of the road. I get stuck for a minute sometimes
I'd definitely try using the newer snapshots. You will see our frustration, as touching the fence even slightly will knock you off.
You should link all of your tracks to one set of textures/objects, so you dont have to re-upload all of them everytime.