I also found this product called Novus plastic polish. We used to use it to refinish the play field on Pin Ball machines.

http://www.novuspolish.com/fullscreen-launch.htm

I have used it and my headlights were completly clear again.

'97 Mercury Mystique GS (Not mine anymore...) Now running a Toyota Matrix XR Red, 16" wheels, Sunroof, VVT-i