If you have heavy pitting from sand etc you'll have to also wet sand. Sounds like Plastx is a great product. I have it on my list and will use on a regular basis to keep the headlights performing well.
Here's how I did my 95 Corolla and 96 Voyager minivan.....
Jay in MA
====
1. When wet sanding, dip the paper in clean water often. You can also re-wet the lenses during the sanding process using a spray bottle.
2. Using straight horizontal strokes, wet sand the lenses with 400 grit wet/dry sandpaper to remove all deep pitting and even out the lens surface. If you have heavy pitting or severe clouding/yellowing, start with 240 grit. It will save you a lot of time and elbow grease. This phase is complete when all of the deep scratches and pits are removed. They should be very hazy at this point but consistently hazy.
3. Follow up using the same process but graduating through 600, 800, 1000, 1500 and 2000 grit paper. Depending on availability, you can skip some of the grits but it might require more sanding with the grits that you choose. They should be looking good now...shiny when wet but very hazy when dry.
4. Using a fine rubbing compound, buff the lenses to a nice smooth finish. Buff again with plastic polish following the instructions that come with the product. Meguire's PlastX and Novus will work well to polish them to a like new appearance. Try to use a polishing product that contains a UV protective finish.
5. I finished mine off with a coat of the Gel Coat product and was very pleased with the results.
I ordered two 10 oz bottles from online from an e-Bay seller. It came to $16 for me which includes shipping and handling.I will give it a try on my yellowed plastic headlights.