I've been without a screen protector for about three years. I always end up with very BERY fine hairline scratches, visible only when viewed at an angle with the screen off and you have to be liking for them. I'm not going to say it happens to everyone since I'm sure someone will argue that it doesn't, but I can't imagine why I would be a special case; phone is always In my left pant or coat pocket with nothing else alongside it EVER.
Anyway, I don't feel screen protectors are necessary anymore unless you want to be sure you keep your screen absolutely pristine.
A case, on the other hand, is a little different since even that few inch drop can potentially ding or dent the metal. But that depends on whether a ding or dent bothers you. I have a leather case that's scuffed up some, but I like the look and even the scuffs take in a great patina. I actually didn't get a new case this year because I love the look and feel of the one I have now.
TL;DR: I think a case goes a long way keeping scuffs off your phone. A screen protector is no longer necessary unless you want to insure a mint condition screen.