For an OTC product, I used Mothers Back to Black. It worked good for me on my wife's 2002 Nissan Xterra. The Xterra hadn't been detailed in a very long time, and the bumpers and plastic trim were very faded.
I applied it liberally to the plastic surfaces and it lasted about 3 weeks (and a lot of rain). After 3 weeks, I reapplied. The second application only took a few minutes since the trim was still in much better shape then when I first detailed the auto.
On the smooth plastic trim (front grill of the Xterra), it was useless. It didn't soak into the plastic and change the color.
Anthony - will waxing the front grill (smooth very hard plastic) of the Xterra change the color back to its original color (or close)? It seems to have spots on the plastic that are darker like some type of oil dropped on it. I have had no success cleaning these spots off.