i have heard toothpaste will do it although have never tried. I bought a headlight restore kit before for a toyota and it came with three sets of wet sand paper all in the thousands but it also came with a sealer and it worked really well just takes time.
This is what my friend does. He wet sands all the way down to like an 800 or 1000 grit. This leaves the light nearly opaque. Then he puts on a good layer of clear coat. Once dry the leadlights look like new. The reason for a thick clear coat is you can sand out any minor imperfections and still retain a clear headlight.
my buddy did this to a mutual friends Infiniti. First time he used a restore kit but after a week of good rain it looked terrible again. Since the sanding and clear coat they still look good as new!