I upgraded from a 12PM to a 14PM in June. Mainly because I felt the camera upgrade was significant enough (not just another iteration of computational photography). I'm happy with the photo improvements. The Magic Island is meh. I think I prefer the notch (or no notch at all), but I do like some of the information the MI displays. However, I don't really interact with it like I thought I might given all the hype it received around launch. What really surprised me was the ProMotion display. Like some others, I thought 120Hz was no big deal just marketing fluff. Maybe it is for some people, but I really notice and prefer the higher refresh rate. All the animations and scrolling are noticeably smoother. True, if you don't know what you're missing or you are used to 60Hz, nothing wrong with that. Going back to my 12PM the display makes the phone "feel" older because of the lower refresh rate. Camera and ProMotion may not be enough for someone to upgrade, but these two things made it worth it for me. I usually keep phones for a minimum of 2 years before upgrading, but with the 14PM I will likely go for a longer refresh cycle.
What I miss about the 12PM: The 12PM is noticeably lighter than the 14PM. Not enough for me to go back to 12PM, but iPhones are getting heftier (until 15PM). Also, the camera bump is getting obscenely large. Makes the 14PM feel "top heavy" to me and just looks borderline ridiculous. And I thought the 12PM camera bump was bad. Having said that, I'm begrudgingly living with the 14PM camera bump because of the improved camera performance. The other thing I miss is the physical SIM. I've adjusted to life without the physical SIM. I don't travel so much or require a physical SIM on the fly. I did have to change from Ting Mobile for my second number because for some reason they don't support eSIM (even though Boost Mobile supports eSIM and DISH owns Boost and Ting - I went with US Mobile for my second number).
Lastly for what I do on a phone, I don't notice a difference in performance, so the CPU and Memory updates don't really matter much to me at the moment, although I'm happy to have the upgraded components.
After all this blabbing, bottom line: Improved display (ProMotion and Always On) and camera (48MP and computational improvements) led to me upgrading my 12PM to 14PM. I miss the 12PM lighter weight, physical SIM, and smaller camera bump, but wasn't enough to keep me on the 12PM for another year. If I hadn't updated to the 14PM this summer, I'd likely upgrade to the 15PM which has all the 14PM benefits plus USB-C and comparable in weight to the 12PM.