My Camry had one of the worst cases of hazey, UV damaged headlights you could get. I had to buy Xenon light bulbs to get enough light to come out. One day, I was waxing my car but accidentaly used "TurtleWax" buffing/polishing compound instead. I spilled some on one of my headlights, buffed it off expecting the worst, and was shocked to find that the headlight looked to be in much better condition. Of course, my eyes could be playing tricks on me.
To make a long story short, I've found that buffing your headlights (and taillights) with a polishing compound seems to make a noticable difference. Of course, it won't repair internal UV damage deep inside of the acrylic, but I would assume that most of the damage would be on the surface anyways. It sounds weird, so if anyone else wants to try this to hopefully confirm my story, please do. Keep in mind that I have a 92 Camry, so if your headlights are the clear type, are in excellent condition, or are very different from mine, I wouldn't recommend this. Also, make sure you use the BUFFING or POLISHING type of chemical, NOT waxing. The buffing/polishing chemicals contain a very mild abrasive that will remove oxidation and microscopic pits, which is why I think it helps the lights.
As a side note, buffing compound does wonders to oxidized or stained paint. My Camry looke dawful for a while... No gloss at all, stains streaking down the sides that would not come off with soap. If you've got crummy paint, try this stuff. My car almost looks like new now. Make sure you put on a few coats of wax after using this stuff. It's very important for preventing furthur staining and damage.