I might be the opposite side of the scale here but I love upgrading my iPhones. It keeps my kids happy as well. I'm glad they last as long as they do too and for as much they are used and abused, they have been incredibly durable and worth every penny, IMO.
I go all the back to the iPhone 3Gs and have been upgrading roughly, every 2 years since.
This last go around, my wife and I upgraded to the 8 Plusses and we sent the 6 Plusses down the line to our kids. We took their 5s's and sold them to buy our 3rd child, 11 at the time, his first iPhone with a contract and data, a used 6 Plus so he had the same phone as his siblings.
This Fall we'll do it again.
The kids will get our two year old 8 Plusses, we'll sell the 6 Plusses and get the youngest his own used 8 Plus and the wife and I will get the latest offering whatever it may be.
Wash, rinse, repeat.