One issue that worries me with going the old flagship route is the lack of support. I was checking out the LG G2 recently for one of my relatives and I was shocked to learn that it would not be updated to the new interface of the G3. That's the good thing with Nexuses, you usually don't have to worry about those things.
Also the G3 mini was just announced a couple of days ago. It could be interesting, although the price hasn't yet been announced.
Regarding carrying a spare battery, I think that to be fair the N4 and N5 have a bad battery life compared to other flagships. It seems though project volta will have a big impact on battery life, and hopefully future nexuses, if there will be any, will pack larger batteries. I doubt however that I won't have to charge the phone every night.
Also the G3 mini was just announced a couple of days ago. It could be interesting, although the price hasn't yet been announced.
Regarding carrying a spare battery, I think that to be fair the N4 and N5 have a bad battery life compared to other flagships. It seems though project volta will have a big impact on battery life, and hopefully future nexuses, if there will be any, will pack larger batteries. I doubt however that I won't have to charge the phone every night.