I work hard in many areas of life to practice contentment, even with my audio hobby, so the following should be taken in that context.
If upgrades were no longer possible I'd be totally pissed off. I am a system builder, not just an audiophile. There are definitely two kinds of listeners, those who slap something together and those who strive to develop rigs. I am the latter. I get as great satisfaction from the development of the rig as I do the listening. I develop rigs not just as a means to an end, but for the enjoyment of exploration of what the result will be. Some people cannot understand that and discount it as not being an audiophile. I could argue the opposite and suggest that those who give little time or attention to the gear are not much of an audiophile.
I have spent decades messing with different gear, dozens upon dozens of rigs. I love doing this! Of course I want improvement, and if improvement was no longer possible, then it would be like the death of the hobby to me in this important aspect. I would not enjoy the hobby as much if I could not tackle a new set of gear, a new "formulation" to the system. I could always go back to working with budget gear, but having worked with higher end stuff that would not be very satisfying - like moving from the Rockies where you can ski for ten minutes or more nonstop down the mountain to a flatland locale where the biggest hill takes 20 seconds to run and more time is spent on the ski lift than skiing; not so exciting. When your ears have heard what seems exceptionally life-like sound, they want it all the time.
Could I adapt and adjust to a life without upgrades, without system building? Yes. But it would not be fun and I certainly would not like having the joy of building systems to improve taken away.
Perhaps if technology stood still I would have just cause to say I'm content to not search for improvements. But there are always improvements, always new systems which will best the old. If I had simply been content to hook up some gear and delude myself into thinking, "Wow! This is probably close to top end sound," I never would have had the experience of blowing through multiple levels of sound improvement - and the ecstatic experience of hearing/enjoying the music that way.
So, as a system builder I ask: Why would I want to stagnate in this hobby? Why should I succumb to sameness? No more upgrades = no more improvement. I would hate it.
