If you get the case you are still going to have the problem with dirt and dust getting in there and that is what causes most of the scratches anyways, I am pretty sure that you wont take a set of keys and try to scratch the hell out of it, but if you did with the InvisibleSheild (made by Zagg btw) or the BodyGuardz on it, you wouldn't even scratch the surface. I have the InvisibleSheild on my iPhone and it still looks like the day it came out of the Apple store.
So short answer get the coating. Why would you want to cover this beauty up with a case anyways.