I have used Meguirer products...
I have used Mequire(?spelling?) plastic cleaners/polish products before with great success. On several old boats with old yellowed and scratched plactic windows, I was able to wash them, then use the cleaner and polish to get them look like new again. They have a cleaner wax which 1st removes most of the dirt, scratches and yellowing. Then the polish really brings out the shine and make them look like new. It takes a bit of elbow grease but after an hour or so, my old dodgers were nice and clear again. I then just use some polish about once a year to keep them in good shape.