For all those that have yellowing and pitting on your headlight lenses, I have the solution for you. I REALLY wish I had taken the time to get some before and after pics. I'm really impressed with the results.
My driver's headlight had gotten all yellowed and foggy and wouldn't put out much light. I've tried those cheapER kits that have the polish/buffing compound integrated into the buffing wheel and got OK results. Yesterday I had to replace one of the bulbs and figured "what the hell" and bought the Meguire's Headlight Restoration Kit (P/N MMM 39008). It comes with a velcro wheel to mount to a drill (HIGHLY recommend a cordless. Corded may be too fast.), sanding pads (500, 800, 3000), the buffing wheel and a bit of rubbing compound. When I started I was getting worried because it looked TERRIBLE. I didn't think I'd EVER get the lens clear again.
You start with the 500 grit pad and get rid of all the pitting, yellowing, and any other imperfections. It is VERY important to take your time and follow the directions. (Especially the masking off the surrounding sheet metal part... I didn't hit the sheet metal, but I did hit the bumper. Left a nice scratch...) I will warn you, at this step, it looks like you may be buying yourself a new headlight... Oh and don't spend too much time on one spot. You CAN smear the plastic. Which will look awful for one, and two you'll be doing a lot more sanding.
Once all the pitting and yellow is gone, you move on to the 800 grit pads and get rid of the coarse 500 grit scratching. With the shape of the 02-05 headlights, this can get tedious. Getting the dip between the "bubbles" in the lens is a PITA. Sand until all the 500 grit scratches are gone. Things are starting to look a little better...
Once that has been completed you move on to the 3000 grit pad to remove the 800 grit scratches. This is the wet sanding step, but I found that if there were still some deep 500 grit scratches left over, just use the 800 grit wet, and by hand to bring them down a little more. I had to bounce back and forth with all 3 pads to get it pretty clean. At this point some of the clarity will begin to return and your sense of panic will diminish slightly.
Once you're satisfied with the clarity and there are no more scratches left, move onto the buffing wheel. Add a little bit of the supplied rubbing compound and buff away. You'll see the lens start to clear up dramatically. Usually this would be the last step in the process and once you've done it, it looks pretty good. I took it one step further and used some 3M Clear Plastic Polish to finish it off. From 10ft the light looks almost new. I still have a little bit of dullness in some areas, but the bubbles in front of the bulbs are clear. I think if I'd had more time and patience, I could have gotten them to a brand new level.
If you don't have the money to replace your lenses and have the patience to do this, you won't be sorry. I spent $18 on the kit and another $15 on the polish (3 months previous). If your lenses are REALLY bad, it may take more than one kit to do. I was lucky enough that one kit did it. Well worth the money in my opinion.
Sorry for the long read, but I had to share my success. Maybe this should have gone in the How To section... I'll let the moderators decide that...