Your stock cobra wheels came with a clear coat of urethane. Unless the coating is turning yellow or wasted, I wouldn't put a polish on it, since that will start taking off the finish.
When I bought mine they were filthy, so I took a day off, (yeah, I'm like that), washed the big stuff off with simple green and a brush, but there was still lots of tar and old dust on them. So I soaked the backside with WD-40, let it sit, and then went over it with a rag, my fingernails, and then some wax to finish it off. They looked NEW after that, and 2 months later still look damn good. Pop them off, spend some time and elbow grease and get in there and clean them. You'll be so happy, and you'll want to show everyone your rims.
I agree with Max on this. I've always used Meguiar's on my wheels. I do the three step process (cleaner, polish, and carnauba wax). I do this on the wheel face as well as inside.