I just purchased a 95 gs300 and the outside lens were so faded, you could not see the bulbs inside! Years ago, I heard about people using Brasso, a metal cleaner you can find just about anywhere. They used this stuff to clean plastic faded lens, so I figured I'd give it a try. After 3 applications, they came out 95% clearer! I could see my 300's pretty eyes! ;) The previous owner had the rear painted and some overspray of clear coat got on the rear lens. This stuff disolved it and made it like new. Afterwards, I applied Mother's Gold Class on all the lenses to give it a layer of protectant. I really thought I was going to have to buy new headlight lens due to the drastic fadeness. I did this to the fog lights too. Just a tip for you all that really amazed me. I don't have before pics, but I will post some 'after' shots soon.
DISCLAIMER: I TAKE NO RESPONSIBILITY FOR DAMAGE DONE TO YOUR VEHICLE. THIS METHOD WORKED FOR ME AND MAY OR MAY NOT WORK FOR YOU.