Interesting thread. I have ended up exactly at the same place, though coming from an entirely different direction.
Having neither the budget nor the desire for Apple's newest and shiniest toy, I stay instead a year or two behind (sometimes three), buying that model used and keeping it until obsolescence starts looming on the horizon. Then I buy, sell, and start the cycle all over again. I have saved thousands of dollars this way.
(I also use a dirt cheap phone service that gives me 6 gigs of data and picture perfect coverage --even when I have found myself in the middle of exactly nowhere--, plus free international calling, for $36 a month.)
All those years, I liked that Apple kept the size and form factor of the phone more or less the same, just making it slimmer and lighter and enlarging the screen. It is the perfect size for slipping in your pocket or keeping in your hand. When the iPhone 6 first came out, and then the 7, I did NOT like the size, or the way it felt in my hand. (Not to mention all that glass --really? Bigger and more fragile?)
I also use the Mophie power cases, which not only give you extra juice but are great for protection, and they bulk up the phone considerably. Carrying around a model 6 onward in a Mophie case would be like carrying a frigging tablet.
My time-proved routine, alas, got a monkey wrench thrown in earlier this year, when my iPhone 5 developed a case of the swollen battery, and then the technician who replaced it killed my phone in the process. Faced with the imperative of having to purchase a new phone for the first time in ages, I did my research (whilst using an El Cheapo Android phone as a temporary solution; not a nice experience, I assure you) and opted for a refurbished SE. (Overstock had a good deal on those.)
And boy, am I happy. I have last year's newest and greatest (more than good enough for me) in a time-proven form factor; I have a phone that basically does stuff that the newest and shiniest can't anymore (like TouchID); and I was even able to keep using my older Mophie cases. For me, the SE is a winner all around.