Here I used the Cera Kote headlight restoration kit (about $15 from Wal-Mart) and i was really surprised at how much of a difference it made on my OEM headlights. All factory from 2002, so I didn’t expect them to turn out that great, but it’s amazing what a little smoothing and sanding can do for old headlights. I wish I had taken better before and after pictures, to be honest, but this speaks for itself!
I’ve also been very impressed with Cera Kote trim restore products before, maybe I’ll show some pictures of what it did to my engine-bay plastics. Stay tuned!
Update: it’s been 7 months so far, and still looks great. I’ll see what it looks like after a year and post pictures of that too. My car gets a lot of UV exposure since it’s not in a covered environment, but it holds up well. I think the coating you apply at the end must have great UV protection
For headlights specifically: both. A cleaner/clearer lens will greatly improve headlight brightness assuming everything else is working as intended.
If you have a car that has headlights like the before pic on this post, I'd highly recommend grabbing a kit.
Also the box said 10 horsepower.