Really? I'm not a guy that needs a ton of stuff. BUt I like to store music as I live in a rural area so I can not always connect to spotify/play. Also nice to be able to have a back and some roms for quick flashing.
I hear the N4 was pretty bad. I am perfectly happy with the build quality of the N5. I can't think of any current flagship that I would run without a case. IMO they are not really meant to be ran like that unless you work in an office or something and are super delicate with it.
I have had a gnex and an N5 and dropped both plenty of times. I just use them with a thin tpu case. Neither has broken. If you run the phone naked well then of course any phone can break from a short fall depending how it lands.