It certainly hasn't for mundane tasks like browsing the web or playing simple games. I recently bought a 10 year old 21,5 inch iMac for my kids for around the price that a same sized, also full hd, brand new screen would cost. Only that screen doesn't come with built-in i5 CPU, SSD, Gigabit and AC networking. It replaces a 2011 Macbook Pro only because I want something stationary for them and not something they get tempted to lug around and drop on the floor. Apple doesn't allow the latest OS's to be installed (though there are ways around that[0]) but I haven't felt the need for it.
So unless you need raw performance or extreme power savings because you run your device 24/7 there should be no need to get the latest and "greatest".
The majority of phone users use zero features - with the possible exception of the camera sensor - that where not also available at very high quality in 2013.
For phones, I currently see zero reason for further hardware upgrades.
Not to mention that the newer devices yield considerable utility and efficiencies that make older devices redundant.