When I started in photography in high school in '86, my dad gave me his Fujica AX3. I later I wanted something with autofocus, so got a Canon Elan around '97. Somewhere around 2000, I upgraded to an EOS-5 and later got an A2e for a backup body (they are basically the same thing). That's as much as I figured I need for my main film camera. There were higher level pro cameras, but not anything I felt compelled to get. I then got a 10D a few years ago when I went digital. I don't plan on upgrading that anytime soon, as it does everything I want. Down the road, I may get one that has a full-frame sensor.
Through all that, I played around with a bunch of other cameras. None of them I considered upgrades as they weren't my main use camera long-term, but they were all cool to take pictures with.
For film cameras, even though they kept coming out with newer models, it was often hard to justify "upgrading". The EOS-5 came out in '92, and if I hadn't gone digital, I'd still be using it for my main 35mm camera. I'd also be using cameras a lot older than that (I loved my
Agfa Clack).
For digital cameras, the tech is moving so fast that the lastest and greatest
is more noticably advanced. The trick is to decide what you want and stop there. It's really easy to be tempted to get the next one. When the 20D and then 5D came out, I purposely avoided reading anything about them. Lately I got curious so I did look up the specs. Luckily I don't feel compelled yet.