Yesterday, I used the 3M Headlight Lens Restoration System, part number 39008 as well as the 3M Quick Headlight Clear Coat, part number 39173.
The results exceeded all of my expectations. The plastic housing lenses are crystal clear, probably more so than when they were new. It took me about two hours to complete the job using all of the abrasive disks in the package and stopping every few minutes to wipe the dust off the lenses. If I had to do it again, I'll probably be able to do it in an hour.
Of course, the question now is, how long will it last. I'll know eventually, but I have lots of confidence in that 3M clear coat product, and I don't expect to have to do this again for at least a few years.