i found an excellent rubber and vinyl [plastic] dressing @ www.griotsgarage.com and wanted to give my impressions.
i got an 8 ounce bottle of Griot's Rubber & Vinyl dressing to try on the interior plastic to cover mars/scratches on my '08 xB - as we all know, they mar/scratch fairly easily...
i had a mar about 4 inches long on the surface where i rest my left elbow on the door panel and applied the dressing and was pleasantly surprised. not only did it completely hide the mar but it blends well with the door panel color. it is non-greasy and has a flat satin finish. their products are not inexpensive, but they are high quality. see the pic below - the top surface was treated and the lower was not - both look the same and mar is gone:
It contains no harmful silicon oils, petroleum distillates, waxes, or other dangerous solvents that can harm and dull the surface of vinyl and rubber over time.
i also tried it on my tires and it gives them a nice satin look:
you can find the rubber and vinyl dressing and Griot's other fine car care products here: