Just be sure and use a clean, wet washcloth to clean them. The finish is really no different than the painted finish on your car, it will scratch just as easily. I would not use wax due to the high temps, just keep them clean...
I agree with bergenfelter. Just take the time each wash to run the cloth around the outside. Also, I have a wheel detailing brush that I swab around the inside as far as I can get up the pipe (geez, does that sound nasty). LOL. Mine stay shined up. I would not wax them, it can not handle the heat and will probably yellow and bake on.
I am an avid user of Stoner Car care products. I use their glass cleaner on the tips. Mine shine like a mirror.
Incidentally, for you guys that like the shinny look on tires, their More shine less time tire dressing is the best I have ever used and I have used MANY. They shine even after driving all day. Takes a few rain storms of driving for it to wear off too.
Much like the honda spray cleaner/polish I mentioned on a another thread, I have another motorcycle cleaning product that I would put money on is better than anything else you can use to clean metal/chrome/etc. It's called a "classic cloth" and it works unbelievably well. It's an actually cloth coated in some sort of chemical wax type stuff...it feels kind of greasy to the touch. Well you rub it all over a metal surface, the harder you rub the better it works...it'll leave a greasy film over the metal. Let it sit for a few minutes and remove/polish the surface w/ a microfiber cloth. The cloth will get BLACK marks all over it from the oxidization and dirt being removed. I use it on my gold chain too...works soooooo good. I used it on my rims, the frame on my bike, any unpainted metal surface.
Classic cloth...get on eand you'll see what I mean.