How long do you or should you keep your gear.

I think there are two of kinds sound equipment enthusiasts, automobile buyers and hobbyists. To automobile buyers sound equipment is an appliance. You buy the best your income allows and drive it until your income improves or you get tired of looking at it, and then you drive the next set of gear. The hobbyist is on an endless quest for a new aural experience. It is like a heroin habit, if your habit was limited to your income and you could sell your old heroin. Because the absolute sound is unreachable, the pursuit is infinite.

I myself have always been an automobile buyer, and due to various career hiccups I was driving an old banger for the longest time. You are probably familiar with this kind of setup: Quality brands but the cheapest thing they make. Musical Fidelity amplifier but the old shoebox-sized one they used to make; Sota turntable but a Moonbeam bought used, that sort of thing. Lately through improved circumstances I have moved up to what I like to think is a gentleman’s mid-fi, which I suspect I will be driving for the rest of my life. If I spent half as much as I do on records I’d have something much better in the electronics line, I think, but such are my priorities.

I occasionally remind my wife that I don't hunt, fish, nor go to casinos..  And I tend to replace my audio equipment very infrequently, so I'm a relative bargain.  😄  I just replaced 31YO Counterpoint amps with PrimaLuna EVO 400 amps, but I kept my 31YO Dahlquist DQ20s, as I didn't hear anything compelling enough to replace them (without spending $20K+)..  The addition of a Rel Acoutics 8/12 subwoofer facilitated that decision.  

Rather than how long does one wait to chuck stuff out, a more interesting question for me is how long does one wait to release/buy new (not necessarily better, could be just another version, perhaps worse) technology.

They are two completely different issues.

Another alternative, Carlsbad, is to focus your time and energy on improving the sound produced by the gear you already own.  This can be a lot more rewarding and considerably less expensive.  A different kind of challenge...