> but I will use it until some component fails in a terminal way
This is what I told myself too, but I also upgraded after 3-4 years after being annoyed at just how slow my phone was (or to put it another way, just how much CPU power apps demanded now). The phone still works perfectly fine, it just slows down to a crawl right when you're in the biggest hurry. (e.g. at one point Google Maps took multiple minutes to refresh the screen right when I was driving and trying to figure out the right directions, and I still haven't been able to reproduce it, but I sure as heck don't want to live through that experience again.)
Nope, I don't mind how much my phone costs since I use it daily, but I will use it until some component fails in a terminal way. I had a Note 3, swapped its display module once, but it finally died. It lasted maybe three or four years.