funny this came up today, i just did one of my headlights. they werent yellowed, but they did have a hazy look. i used 1000 grit, 1500 grit, then turtle wax rubbing compound, then i used plastx. dont look brand new, but look much better.
the reasons they dont look brandnew isnt b/c of the methods. had i spent more time (i didnt have enough) they would look almost brand new