There are many ways that the Slot Car program could be extended (like, maybe, something other than a random speed control? :-) One that I think would be particularly interesting in a classroom setting would be to use the Slot Car Program as a vehicle for exploring distributed objects.
I think it would be interesting to make a two-player distributed slot car program, probably based on RMI. Perhaps a Scrollbar could be used to set the speed. Each player would be at one workstation, and a central server would coordinate the two players' views. OK, so it would be a pretty lame video game, but as a classroom exercise in distributed objects, I think it would be fun!