I was thinking maybe that HO racetrack of yours, looks like you could make some landscaping, maybe guard rails, etc with it. Pretty cool, looks like it is sort of a controlled hot glue gun!
It's as though you read my mind. Simulated overhead power lines, fencing, etc... I haven't had a chance to check to see how much they cost or what the raw plastic costs, but I'm planning on getting one if they're not too pricey. I'm still trying to think of ideas for a full sized vehicle.