Novus makes well-known plastic cleaners that will work. Novus 1 (a spray) will clean the lightwedge just fine. Novus 2 (a cream) can be used to buff out fine scratches. Novus products are standard stuff for maintaining plastics in the pinball industry.
On a side note, Sony is releasing new booklight covers for the 300 and 600--but neither is a lightwedge. Instead, they have fold-out LED lights, with a battery holder along the spine.