This thread gave me an idea. So I have started to build up a track builders asset library. If you have anything you would like to add then post it here and I will include it. This could include 3dsmax GMotor Materials, animated objects, static objects etc etc...
In future I would like to build a test track with experimental objects of all kinds (water, grass, animated crowds etc..) Kind of inspired by what they did with the UE4 editor: (demo starts at 3:01s)