My last few phones have all developed a ropey micro-usb connection after daily use as a satnav. I'm hoping either USB-C or wireless charging will solve it in future.
IMO - 2013 flagships (say Snapdragon 600, 2GB RAM) had enough grunt to do what most smartphones currently do. Higher resolution displays are needed to justify better specs, which in turn leads to the drive to bigger phones. Anything much over 300ppi is fine for a phone screen. Tablets exist - ergo I have no interest in big phones. A 720p 4-4.7" phone is fine as far as I'm concerned.
Because phones are in constant use, they get a battering. I typically find my smartphones suffer from wear and tear that compromises usage within 2 years. That will keep a demand for handsets but not necessarily upgrades. I seriously considered a side-grade this time.
Asking myself what I wanted a phone to do better, I came up with battery life, durability, more available storage for apps, speaker quality. It's nothing revolutionary. Really all my smartphones have just done better and faster what my HTC desire was doing in 2010.