I still have not ordered my replacement hard coat for a variety of reasons, but I did have some time alone yesterday where I could remove the lights from the car (with overlapping purpose - I also want to see why they shake around in the body so much) and wet sand them.
I started with the foglights which actually looked like they turned out OK. I'm not "done" because I'm not completely pleased with the results on the headlights, however, but here's some things I observed yesterday.
1/ it's easier to work with the headlights out of the car
2/ For most of the lights I used 600, 1000, 2000 grit papers followed by a variety of liquid compounds/polishes. On the last light I did something more like 320-600-800-1000-2000 to see if there was any improvement (there wasn't, but the 320 worked quicker to level the major defects).
3/ The factory hardcoat is actually quite thick. There were some cases where over the entire surface of the light I had leveled out most defects and only a dime or quarter sized area of the hardcoat was fully removed.
4/ None of the articles I've read have mentioned it, but I'm suspecting that you probably need to be sure to remove all of the coating if you're going to go through it anywhere. I can really see a difference in the plastic where the coating is fully gone and where it's not. Of course this may not be a factor if I had my topcoat on there. On the other hand it might be because I doubt it's identical to the factory top coat so it might still look somewhat different.
5/ 2000 grit was the finest paper I had on hand, and the finest I saw on most store shelves. For some reason, I couldn't remove 2000 grit marks even with Menzerna SI 1500 (super intensive polish) and a pad on a drill (improvised rotary). This surprised me. I tried Menzerna SI 1500, PG 2500, SF4000 and Menzerna metal/plastic polish by hand and machine and the 2000 grit scratches remained to some extent. I did manage to find some 3000 grit paper (which seems like almost ordinary paper) and I'll get back to it. I found that Meguiar's plastic polish (#10) contains enough glazes to fill it in and look "OK". To most people it probably looks world's better than the sand and rock blasted condition they were previously. To me, a sorta detailer, sanding marks look worse.
6/ I lubricated with Optimum no rinse wash mixed to 'clay lube' ratio
7/ I found my 3M paper degraded faster than expected considering it was used on plastic. I needed multiple pieces to complete each step because it became ineffective. I was rinsing the paper out so I don't think it was simply clogged.
8/ I used a "cross hatch" method, alternating lengthwise and up/down sanding as I moved between each grade of paper instead of rubbing in circles. In theory I thought this would help (use the paper until you see no trace of lines in the perpendicular) but...
So, the biggest lessons may be:
1/ if you compromise the coating anywhere, make sure you remove all of it. It's obvious looking at the lens if this is happening.
2/ 2000 grit marks seem harder to remove from this plastic than I think they should have been.