You speak the truth, my 04 S plastic trims look like new. Its once you dont regularly wash the car and start applying products to the trim that they begin to fade really quickly. I didnt apply any products to mine for well over three years.
Megs Endurance tyre gloss gives a good shine on trim but it doesnt last. Megs Plastic Care is useless on the Mini. And Tried Autoglym and wasnt impressed on the Mini's Plastics.
Best Ive tried to date is Mini's plastic care (Think its the right name). On a clean cotton cloth and wiped on.
Mates GP's arches where going brown on him and he had tried several things and was going to get them replaced under warranty. I let him try the Mini stuff at a Mini Show this summer. Brought them up like new, and it seems to last pretty well on mine.
No Idea on price as I got a bottle of it free with the GP, thought I might as well try it out.