I'd try Scratch X first before I'd sand anything. 3M also makes a very effective Plastic Cleaner that I've used with success even without the Porter Cable. As I said above even the replacement lenses haze and etch. I treat those lenses like my paint, they get polish once a month and a detail spray after every weekly wash. Ever since we've noticed this problem I make a mental note to look at other cars and I see this on a lot of vehicles, not just ours. One more time, the solution is a Porter Cable, orange cutting pad and Meguiars Scratch X. You will be amazed.
Pat