We have diamond plate in our kitchen as our sink back splash. I've never cleaned my Rectos diamond plate, but the wife uses a a mixture of water and vinegar and the diamond plate cleans up perfectly. Not so much a polisher per se, but it definitely cleans up nicely.
Not to hijack your thread, but I just had an idea. A recto would look cool if you could give it an oxidized/distressed treatment. Make it look tarnished - almost like the Jerry Cantrell Wah pedal. That would be cool, don't you think?
Blue Magic wheel polish works the best....works absolutely amazing in cleaning nickle hardware on your favorite axe as well (especially the delicate PRS hardware...nothing works better than this on those guitars for some reason)