I'm essentially there now.
I've never actually heard a better sounding system, at this point, than the one I have. That does not mean to me that there aren't better systems of course. I just haven't heard them yet. I fully intend to, even if that means some travel. But, I believe that even if I heard better, I just don't think I'd be thinking of what gear to buy next. If I could never buy another audio item, I know I'd honestly be just fine thank you. I may want to buy more tweaks if I get bored, and at some point I believe I will, but as far as audio problems left to solve??...they're all gone...all have been put to bed and everything now is uniformly excellent. It doesn't matter what my expectations are that day before I flip the system on, the sound that greets me is always excellent and fully engaging. And it doesn't matter what the recording quality is or the time of day...none of that matters...I mean when was the last time you heard someone say that about their system?? It's a really hard system for me to actively want to stop listening to.
But then, even though it took me almost 30 freakin' years to actually build it (that's a helluva long time!), I still always thought in terms of having some sort of exit strategy to definitely shoot for...even as I kept having to redefine my budget upward against my expectations, as well as revise what I thought was possible for me to attain for the money - and what I believed I'd be truly satisfied with, as the years went by.
I've recently heard a $10k+ amp, $14k tt, $14k speaker combo that's twice as expensive as my whole system and I heard a sound that was better in a couple ways and not in others. But, the improvement was actually very slight while the betterment of my setup in the remaining areas was substantial. But, does it tug on me that after all I've done up to now that there is something of some performance area still left on the table?? Of course not. Certainly not at those prices(!)...but, honestly, not really at all. I mean I've accomplished everything I set out to do and more. Sure, if I won the lottery, maybe. But, I just don't even entertain such fantasies anymore. The only thing I dream of now is using the equity built up in my home to get construction started on adding on a listening room later this year. Much cheaper and better for me than trying to find a suitably good other home to move to and no, the room won't have to be custom-designed, sound-wise, and not much more than a good choice of dry wall, insulation and dedicated lines need be involved.
I agree with Erik, after some point you end up learning not how to spend more, but how to spend less. That's actually the biggest barrier to the hobby for newcomers, I think. There doesn't seem to be much of a substitute for the direct experience of the hands-on initiation of figuring out how to spend more before you get your feet wet enough to then figure out how to spend less. I'm not sure I would've been as eager to set it all in motion, if I knew from the beginning how much would be involved, how much it would really cost and how long it would take me.
Then again, knowing the end result??...yep, I'm sure I'd definitely do it all again!