There are plastic polishes that might minimize the scratches. Meguirs sells the expensive versions.
I use Plexus plastic cleaner/polish. It is sold at many motorcycle shops as we use it to clean the plastic windscreens. It won't eliminate large scratches but it will make then less noticable. Do not use paper towels when cleaning the plastic window - too rough.
When I bought my 90 Quad they gave a Alfa Clothe , white , very soft the salesmen said to put it on the window before folding the top down,My top looked new for 11 years.. Any soft peice of material stops the dirt from rubbing on the window.