The matte plastic can be tricky but as long as you don't get too aggressive it shouldn't get too shiny. I'd try one of two different approaches: 1) Autoglym's Bumper Care is a dressing-type product that seems to have a tiny bit of mild cleaner/abrasive in it; or you could try 2) Klasse AIO, which won't leave it utterly matte but didn't do anything weird to the similar surfaces I've tried it on.
For the marring, you just need a mildly abrasive product to polish out the tiny scratches. Lots of choices, I prefer the discontinued, but still commonly available, 3M PI-III MG (05937).
