First, WD-40 is not oil, it is a moisture displacement fluid. Second, since we're not talking about sponge tires, I'm assuming it doesn't really soak into the tire, but disolves some part of the tire, and eventually leaches out.
"The point is to make the rubber softer, just like racing tires are MUCH softer than regular road tires. The more grip you want in your car, the softer the rubber tends to be, and the faster they wear out, and the more expensive they are. Not surprisingly, that's a lot like how slot car tires are. ;-)" The point is, rather than fooling with lighter fluid and risking getting all sorts of junk on your track, why not just do the same thing the real racers do and use better tires?
I'm not sure if these three comments where related to silicone or urethane but, just in case it was the latter...
1) Pick up dust and debris very quickly - not from what any of the guys I know have found. Even when they are dusty, they still work.
2) Hard to true without "blueing" them - i.e. quite a tough material to sand, and you'd have to sand them for so long they risk over heating and going hard at the surface - other way 'round, they are easy to true, at least the shore-40 most of the guys I know are using.
3) Promote axle bounce (due to high elasticity) - nope again. I don't think this is an issue with silicone either.
I clean my tires now-and-again with the same stuff used by photocopier repair people to clean the rubber rollers. Between races, I've seen some of the guys just clean them with spit. Not very sanitary but for the most part, it's not flammable.
Randy