I figured I'd post an update on the Metro's headlights. Its been over 6 months now. But, a lot of those months have been winter, so lower temps and not as much sun hours. However, I always park into the sun in winter for cabin heat, so they do see all the sun during the day.
Here are some pics. Its not super easy to see from the pics, but they are a little hazy.
When time allows, I will be redoing the headlights again. This time I'll probably sand them down with 2000 grit like the DIY I read said to do. Then I'll add the urethane. I'll probably also add a few coats of it. I imagine that doing this will build up the urethane thickness and give a longer lasting protective coating.