I am sure that Apple and others want people to buy new smartphone hardware every couple of years, but, over a couple of years, the faster processor speed, better graphics capability, larger storage capacity and/or new features are things that people will actually make use of and not just buy because it is new.
I hung onto my iPhone 4 for a long time, but, when I finally gave in and got a iPhone 5S last year, it works so much better that I was wondering why I had put it off for so long.
And, as hard to repair as they are now, I think that it is easier now. The first gen iPod touch had a soldered on battery that was tricky to replace without overheating components adjacent to the connector. I replaced the battery on a newer one recently and it was so much easier. Then again, part of why it was easier was better tools are available, including stuff from iFixit.