My wheel had small cracks, nothing structural but it looked bad. I mixed up a puddle of JB Weld and let it run into the cracks (flexing the wheel when the stuff is runny gets it into the cracks). Once it set I sanded it smooth and painted the wheel. I know this is a temporary fix, but it's held up well for a year and still looks great.
edit: It also worked very nicely for filling a chip next to the horn button; I just put a large (excessive) drop of JB Weld on the chip and once it set enough to stick I flipped the wheel over so the drop was hanging. Again, let it harden, sand it, paint it. You need a magnifying glass to tell where that patch is.
