I badly scratched up my Sea & Sea dome port (it's acrylic) while diving at Cocos and Malpelo. Lots of current and lots of rock is a bad combination for a housing with a big dome port. A couple of fairly deep scratches (you could easily feel them with your finger) and some shallower ones (you could feel them with you finger-nail).
After doing some research, including some older threads on this board, I decided to try the Micro-Mesh NC-78-1 ACRYLIC RESTORAL KIT (Micro-Mesh) . It's made for taking scratches out of airplane windscreens. It cost $37 and comes with 9 grades of their Micro-Mesh papers (high grade wet/dry sandpapers), polishing paste, detergent, anti-static cream and pads and cloths.
Taking a good stiff drink first, I started the job with 320 grade wet/dry paper, went to 400 grade paper and then started using the Micro-Mesh papers. Each grade took about 3-5 minutes and the instructions were to sand in straight lines only, not circular, and then rotate the dome about 120 degrees for the next grade.
After the first sanding, the port looked like a diffuser (although when I flushed it with water before going to the next grade, it was clear). However, by the time I did the final polish, it looked new.
I highly recommend this product. $37 and a little elbow grease (actually, not much at all) is a lot better than a buying a new port.