Preventing scratches in plastics:
NEVER wipe ANY surface interior or exterior with a dry cloth....period. High quality, dedicated to your car, micro fiber towels, micro fiber wash mitts, applicator pads etc are the only type of fiber that should ever touch your BMW....but never dry. Always wash after use...never use soiled MF towels for a new job.
I have not used cotton for car care in years...its just not as safe or effiecent as a high quality micro fiber.
Basicly using a dry towel you are pushing the dust and grit along rather than picking it up. That is why MF cloths are so amazing when used properly...they actually pull grit into the fibers and trap it on contact, for car surfaces (plastic or painted) you want to use some type of emlusifier (found in waterless carwash products) to break the molecular bond so the grit is suspended safely and picked up gently by the micro fibers. This is why a high quality waterless car wash used properly will not scratch a finish...painted or plastic.
The finest waterless carwash products have the added benifit of having a acrylic polymer sealant ingrediant therefore putting a protective barrier on the painted surface or plastic surface. They also have anti static properties...which help to repel dust and grit.
I have lost track of how many times I have seen people at out door car shows that should know better than wipe a dry paint surface with a dry micro fiber towel. I have seen it done even at Pebble Beach Concourse d'Elegance....the Audi R8 concept car...by the Audi guy...I ran up and gave him my waterless carwash/acrylic polymer spray and two of my professional micro fiber buffing towels to clean the car from the dust and grit that settled on it.
Interior plastic or painted trim is no different...always use a high quality micro fiber towel and preferably high quality waterless carwash... for a interior I spray the towel first...so you dont overspray on the interior...thats the proper technique to apply any product to trim inside a car...put the product on the towel or applicator then apply to the trim piece.
Removing Scratches in plastics:
If you have scratches in high gloss plastic trim, there are products out there for plastics, however you can use (one poster mentioned brasso) a fine polish designed for a painted surface but the polish must be in in the catagory of removing scratches of 2500-3500 grit scratches preferably a pro diminishing formula (progressively breaks down into finer particles until it diminishes and stops working--this style formula will impart a very high luster all by itself) verses a straight grit polish that will stay at a given grit the entire time. This is why Brasso can work nicely...it is formulated to remove very fine scratches on delicate silver and brass items. Brasso is a staight grit delicate polish, its not a diminishing polish.
NOTE: A diminishing style polish is what many pros use to retore polycarbonate plastic headlight lenses after wetsanding with 2500-3500 grit.
Protecting painted and plastic surfaces:
Plastic is no differnent than painted surfaces as far as protecting it...I apply a paint sealant to any vulnerable plastic trim part...it makes it slick and resist scuffs...also grit and dust will not stick and it will clean easier next time. Professional paint sealants are acrylic polymer formulations that bond directly to the surface an give a very slick finish as well as UV protection.
Always better safe than sorry...if possible test in a inconspicuous area to see how the plastic responds to the polish you have chosen.
Here is blog post on some technical stuff bout micro fibers.
http://www.carscratchremoverblog.com...ratch-removal/