Pledge works GREAT On scuffed up plastics also !!!.I've been using Raincoat wax which is designed specifically for plastic surfaces. I think it works better on visors than Rain-X which works best on glass. Rain-X does work though and doesn't seem to affect the plastic in any way.
Another cheap solution if you don't ride in rain very often is furniture polish; keep a couple of Pledge wipes in your pocket for emergencies!