I used to do a fair bit with lightbars from the States back in the day, I used to buy a product from one of the big suppliers over there that was specially formulated to revive and restore domes that has discoloured, yellowed, tarnished or gone mat through dust and sand abrasion. For the life of me I can't recall what it was called just now but it would work like no other compounds, abrasives or other plastic re-finishers. Clear domes that had been used for years on NYPD or other PD vehicles that had turned beige and mat would restore to virtually new appearance, and what's more they would stay that way too. Some of the segmented Federal Signal domes on the old Aerodynics were stupidly expensive to replace so this stuff was really useful.
So, wet and dry followed by buffing with G3 it is then 😉