I don't mind the plastic case either. I am one of those rare people who doesn't put my iPhone in a case. I have seen several drop test videos where even when dropped from a ladder on to cement the only damages were cosmetic scratches and dings. The iPhone 5 screen is very durable and they were only able to crack it after spiking it into the ground like a football player. I have dropped mine without a case several times and I have a few dings and scratches on the corners to show for it. It feels a whole lot better in my hand and my pocket naked than it ever did with my old otter box cases though. Why buy these beautify designed devices just to cover them up with a cheap plastic case? The way I see it, they were designed to survive without a case or they would come with one in the box.
Anyways, the point of all that is I think colored plastic would be more resistant to visible scratching. The main reason you see the scratches on my iPhone 5 are because they are silver and the rest of the phone is black. If you scratch these polycarbonate iPhone 5Cs you will just see more of the same color underneath. This is colored plastic not a painted on layer.
If I were upgrading from an iPhone 4S or older device I would strongly consider the iPhone 5C instead of the 5S. The iPhone 5 camera is good enough for me, I don't care about the finger print scanner, and it's not like our apps are going to abandon every phone besides the 5S and only work right on the 64 bit chip. It also doesn't hurt that for the same $200 you would spend on a 16GB 5S you can get a 32GB 5C. I honestly think I would rather have double the storage than any of the new 5S only features.
I have an iPhone 5 so I won't buy the same phone again in a plastic shell. If I had a 4S or older I think I would be preordering a 32GB iPhone 5C in green tomorrow though.