After you clean them while they are dry spray them down with NAPA's Aluminum brightener. It will make them look like new. I used to use on my aluminum trailer when I had my bay boat. Stuff is amazing but wear gloves and eye protection when spraying it on.
Not sure anything will make galvanized wheels look good. I thought about replacing them with aluminum but it's a freakin trailer. Trailer has aluminum ibeams. I might have to try that NAPA stuff on them.