Upload & Sell: On
Jon, there's nothing wrong with not upgrading, and your opinion is entirely valid for you and for your needs. However, there's a bunch of us out here to whom your opinion does not apply. I can personally tell you that I shot film for 20 years because that's all there was. And I still sought out the best film for a particular image, and I did upgrade cameras when I found that they had better functionality for what I needed to do. It's no different now, except that the tools do improve substantially every 3-4 years.
I've always tried to use the best possible tools within my budget, and my subjects definitely challenge both the gear and the photographer. You don't get many second chances at wildlife in Africa, and my keeper rates for ground-to-air aviation are in the 1% range.
Do I need ISO 12800, VR, and AF that can track a fast-moving gnat in the dark? Not always. But more often than you'd probably want to know about, one or more of those features saves my bacon and allows me to capture an image which older cameras or gear simply would not have been able to do. And right then, at that moment, the upgrade was worth it. Here's a couple of images where advanced features saved my butt:
ISO 12800, fast AF, and nanocoating:
Fast AF and VR (550mm at 1/100):
And last but not least, my 40x60 prints look a lot better from 36MP than they did from 12MP, 4MP, or film.
When faced with a particular upgrade opportunity, some people don't take it because they don't see good value in the upgrade... the cost is greater than the perceived benefits. Some people don't take it because they can't afford it. Some people don't take it because they prefer to know one particular piece of gear inside and out, even if another tool is better, so they upgrade on a slower cycle. I upgrade every time I can: I even upgraded from my perfectly wonderful 200-400 v1 to the v2, simply for the nanocoating and slightly better VR. I upgrade every time I can as long as the gear does actually provide a significant boost in capability.
I don't care how often you upgrade. But please realize that, if you don't understand why I and others upgrade far more often than you do, then that simply means that you don't understand the different needs and preferences of other shooters... nothing more.