In our race cars we used Plexiglas. We used pledge furniture polish. It worked great. It will not remove scratches but fills them in and some times it comes out like new.
One thing to remember is like all plastics will yellow and or go cloudy and all you can do is replace them.
Find some Blue Magic, sold at AutoZone.
It works good on cloudy headlights.
I have a process that brings them back like new, but it is a process and takes about an hour per light.