How long do you or should you keep your gear.

When something moves within your audio system (cd player/turntable) you may have to replace them, as parts failure may render them obsolete.  But if you have really well made speakers that you enjoy then I think you are fooling yourself as to how much you will have to spend to exceed their sound.  I have Thiel CS 6's.  I feel that I would have to spend about 14,000 or more to find current speakers that would be better.  No thanks.  I also own Krell KCT and Krell FPB 300cx.  When parts are replaced and recapped they are the equal of amps that cost way more today.  So unless somebody can convince me through listening that Item A is so much better and doesn't cost a mortgage payment, then I am content to stay with my very good sounding system that is completely full of discontinued pieces.

Still using and enjoying JR149 loudspeakers from 1978. I have recapped them and recently replaced the scuppered foam grills for the 2nd time. In my main system which is largely Naim and dCS the SBL speakers 135 power amps and 2 x Hicap power supplies are 25 years old. They have been serviced and sound glorious to my ears. My dCS digital stack are the old classic series 15 years old. No need imho to keep chasing what's new. HiFi should imho be an investment - not here today and gone tomorrow. Anyway enjoy what you have NOW. 

Back in the mid 80s, after having several other nice speakers and auditioning many others, I got a pair of Quad ESL63s. they served me well for over twenty years and I sold only because of smaller living spaces. Also in mid 80s, I got an Audible Illusions Modulus II pre. and is still going strong as is my Thorns TT of the same vintage.

Other pieces of equipment I've had for some time, still enjoy and plan to keep and use in one set up or another: A pair of psb Stratus Gold I speakers; a ADS Sub10, sub woofer; an old reliable, still great sounding ADCOM GFA 5500 power amp and a Denon 5 disc CDP - still using for a transport/changer.

A few things I had and wished I had back: Nakamichi ZX9 tape deck; PSE Studio II power amp and my decked out HD Screaming Eagle Road King.....

Have been married to the same great gal for 46 years and still counting - sometimes when something is really good it's worth hanging on to😊 Happy New Years......Jim

There hasn't been much of anything that I have ever kept past 10 years or so. The one exception that I can offer is a Carver C-9 Sonic Hologram unit. I only say that because I can switch it in or out of my system. Also, when I own any electronics of that age, changing out electrolytic capacitors is a given! Likely the RCA jacks a close second. Yes folks, caps do age and will eventually cause some sort of trouble. Having said that, I believe there are numerous products made back then that simply slipped through the cracks or out of favor as new ideas came to be. Quad and HT were murderers to a host of already good gear at the time. Then there were victims of one hit wonders>> Sony's El Cassette or digital tape decks never had a chance to make much of an impression. 

This hobby allows you to keep what works for you (and still operates properly) or change in new items as fits your mood.

While I have several new items in my system, I still love my Denon DP-2000 drive and my Stax UA-7 tonearm. These pieces are mid-70s classics so that makes them about 46 years old.

Enjoy what works for you.

Happy listening!