Being in the automotive industry for 25 plus years I can tell you that none of that stuff works for very long... Best bet is to replace them. The aftermarket makes replacement lights etc. for a very resonable price now a days. Some of the better ones have updated reflector technoligy that puts more light where you need it.
You can get the McQuires plastic/healdight polish from C-Tire and it works failry well, or go to an autobody supply ( I went to NAPA autobody supply) and you can get a more agressive polish. This has worked wonders on our two vehicles. One was fairly bad so I also wet sanded with about a 1500 or 3000 I think it was, before the polish. Year and half later they are still both looking good.
If it is yellowish color and on the inside, take it out and pour vinegar into it and swish it around let it sit for a bit and pour it out. Make sure that when you put the bulbs back in it is dry inside. If you can get some thin foam to put over the bulb socket will help it from coming back right away