My rialta was very dirty outside when I bought it.
I used a cheap $30, 7" polisher from "Harbor Freight" and a product called... "3m marine cleaner and wax" (found on ebay). It brought the exterior back to like new condition.
Here's a couple pics of the process. The left shows the area that I had done. The right is obviously, not done yet! GROSS huh?!
It's a lot of work but worth it.