I'm a firm believer in apple care for some of this.
I haven't scratched or cracked a screen ever.
*knocks on wood
I used the Otterbox on phones when I was in the Kitchen all the time... very hostile environment.
But if you land face down on a piece of gravel, I'm really not expecting a screen protector to do much for me. A majority of the damage seems to come from corner and edge drops as I recall (could be wrong).
My biggest complaint is really that the case isn't grippy... I could fix that myself, but I do like a case that won't slide if I set it on my lap. In the end, that's been a very minor issue.
Never felt the need to cover the camera lenses. They are often protected by a raised border on most of the drop resistant cases, anyway, as are the screens to a minor extent.