I don't ride quads (stopped needing training wheels many years ago :hide
but I do trail ride dirt bikes.
As I'm sure you already know, it's just uncoated colored plastic. You can wet sand and compound to remove deep gouges and scratches if you'd like, but using abrasive polishing methods will never get the plastic glossy, like it would if it had a BC/CC paint system on it.
A trick I learned over on thumpertalk, and personally use, is Mop & Glo. After each ride and wash, just add as many layers as you'd like to get the gloss you want. After a few of these sessions, you'll find that you've got a bit of a semi-permanent layer built up, and you may or may not need to re-apply each time.
There are industry specific products offered, but they're usually silicone-based, so you just end up making your ride a slimy mess and a dirt magnet. Alternatively, products like Plexus and/or Honda Spray Polish don't offer near the gloss as M&G. You could also just buy new plastic, as you might be surprised how cheap it is (at least it is in the dirt bike world).
Sounds silly, but I've been riding dirt bikes since I was a kid, and M&G really is the best option. It doesn't make the plastics look fake or gaudy, just new. I take a lot of flack from my riding buddies about how my bike never looks used, but it goes with the territory with being an a-rentitive detailer, like most of us here.
Hope this helps.
