I sold my 8 yr old Honda Accord this past weekend. It was in great shape and the only comment the potential buyer had was how the headlights were very "foggy". Like most modern vehicles, it had the plastic lens cover and over time, they get weathered or "foggy".
I googled on "how to repair weathered headlights" and found this stuff called Crystal View. I found this at Walmart for $19. It took maybe 45 minutes to do both headights, but the results were incredible.
Here's a clip of it:
YouTube - Crystal View Headlight Restorer Defogger Directions
The potential buyer called back, took another look at the car and immediately noticed the much improved headlights and bought the car.
Last thing, if you do this, make sure you mask the painted area around the headlights so that you don't accidently damage those areas.
P.S. I don't work for Clear View, yada, yada, and am not responsible for any damage you may incur. Just wanted to share a product that worked for me.