I've found the remedy to this problem. My reverse light assemlies and tails are pretty dull after 10 years of weather. I got the "Plastic Polish" from Griots. Applied with a soft 100% cotton cloth - rub it until dry basically and 10 years of weather goes away. Not sure if you can tell in the pics. The one on the right had not been done yet. I still need to do the tails...

 

i also found that this stuff called Premium EZ Wax takes that nasty dullness out too. actually, when the guy was trying to sell me this stuff, he put it on there and whiped it off, and it was new again! that is what sold his product.

http://www.premiumezwax.com/

 

Meguires makes a Clear Plastic Polish (#10) that work excellent too. I have used it and had results that look just like your pics Cebby.
It is very hard to find too, I looked in every store I could think of in Las Vegas when I wanted to try it, and never did find it. I finally ordered some online and the shipping was more than the product itself

 

I might sound crazy for saying this as I already recommended this stuff for cleaning up faded black plastic trim, but Eagle One's "Never Dull" chrome polish removed the white faded haze from the taillights on my 90 4Runner. What was strange was that only the top amber portion had this white haze on it. The red portion looked fine. I tried regular car polish on it and it didn't help much. Then, just for kicks, I tried the "Never Dull" and it cleaned them right up!