You can remove the old paint easily with a brush-on paint stripper, or with Permatex spray-on gasket remover (available at auto parts stores). The toughest paint you can apply yourself is spray epoxy. It takes a long time to dry, so find a dust-free place to apply it. Epoxy paint is resistant to scratches and wear, though is not as tough as powder coating. On the other hand, it would likely cost less to buy a new rack than it would to powder coat your old one.