I don't understand nudists or cheap cases. Otterbox defender and Belkin glass screen protector installed at the Apple store and hasn't been naked since.
It depends. I have seen both people with totally naked iPhones in good condition and people with battered thick cases and screen protectors.
I am currently using a slim transparent ESR case, which still has a 1.5 mm screen lip and reinforced corners, without distorting its original look too much.