I did the same thing on my old '92 318. I water sanded it then used Scratch X to remove the scracthes and polish the lens. It looked good but I remember Meguires sells some special stuff specifically made for polishing plastic.
Hey Dave, what kind of polish did you use?
'02 C32 AMG / '07 C280 / '07 CLS550 / '15 JKU Rubicon