Over time, headlight lens will cloud up due to the sun's UV activity. With so many of the newer cars having large surface areas of their lens exposed (as we do with the ATS), I'm wondering if the lens manufacturers have come up with lens compounds that resist this weathering effect? If they haven't, and you are going to keep your car for several years beyond warranty, and if the car is not garaged, I'd recommend that whatever exterior detailing materials you use should have labeling indicating UV protection. Over the last 20 years I have been using such products as Zaino Z2/Z5/ZCS/ZAIO and Blackfire Wet Diamond/Clearseal. However, if clouding occurs, this can relatively easily be removed with stepdown wet sanding.