My headlights were'nt too bad considering their age, but there was some yellowing and a few cloudy areas. Then, last weekend, I sprayed down the entire front of the truck with Simple Green before washing because it got really caked in bug guts after a trip up to Island Pond. I didn't anticipate the baking sun being and issue and even after I finished washing the truck you could see ghosts of where the drips had dried on the headlight lenses.
I had purchased this 3M kit a while back to use on my awful old Accord's headlights but never used it (sold the Accord for the 4Runner)

So I whipped it out today and spend about 45 minutes on the headlights (including masking time).
As I said, my lights weren't too bad so I skipped right to the last 3 steps (2 high grits and a polishing compound). Pretty neat how much yellow crap it takes off. It made an appreciable difference for the 45 minutes of work it took. I might go back and do another round of polishing compound as I think it could be just a touch clearer. But now there is NO yellowing and no more ghosts or scratches. Very clean and clear.
Amazon.com: 3M 39008 Headlight Lens Restoration System: Automotive
No pictures because I don't think it was bad enough to really show off.
Also, yesterday i got to do the thing I've really missed since we've been truck free. I dropped the rear seats. Lined the back with a tarp, and did a ton of yard work. Pruning, weeding and cleanup, making multiple trips to the spot in the nearby cemetery where the town has us dump our yard waste.
Sounds simple but ever since I sold the Land Cruiser (leaving just the Prius and Accord), we've had to haul this stuff, by hand, in wheeled bins to get it over to the dump spot. It was a huge pain that required us to cut thorough a neighbors yard (the neighbor backs up on the cemetery, we are across street from there.). It made every job in the yard twice as hard, and take twice as long with trip after trip.