You can try some things...
Don't let people tell you nothing will work . Novus plastic cleaners can do a great job on almost every type of plastic in the world. I use it on my MacBook, just research it...
Also, if you decide to buy a case, many like the Speck Case seem like they would work, but seem to scratch, because they get all kinds of crap stuck between the case and the "case."
The best thing to do is treat your MacBook like a **** baby. lol,...I basically don't put anything on top of it and those kind of things.
- Brocktoon