I would definitely keep the steel wheels if you have room to store them. I'm not sure how hard it would be to find the correct steel wheels for your car, but I think it would be more difficult than finding the chrome wheels. You never know why or when you might want to go back to the steelies or use them for another temporary purpose, but if it were me, I would definitely hang on to both the steel wheels and the wheel covers. I do like the new wheels, it definitely changes the look of your car, much more sporty/aggressive now.
As far as center caps go, do a search for Mitch Romanowski. He advertises in the Bugle and he has reproduction center caps that are very nice.
Cheers,