I took a look at Google to see what type of wheels come on a stock 2004 Pontiac GTO. From the looks of it, it appears to be polished aluminum. Since it's from the factory, I would assume it is coated with a clear coat similar to what is found on your paint. There are some great articles that explain how to see if your wheels are coated or not aluminum.
Don't worry too much. Regardless, I think that a good polishing would save them, regardless of if it has a clear or not. First things first, however: take some pictures so other, more experienced professionals may comment on your situation. Mike has given some great advice regarding before/after pictures if you have them. Also, it never hurts to call or email the manufacturer. They know their product better than anyone.
In the future, if you want to go the OTC route, aluminum wheel cleaners are generally more gentle than all-wheel cleaners. I know this sounds crazy since all-wheels include uncoated aluminum but it's true. Just FYI...