How good is good enough?

I'll add that I also have a full rack of gear (sitting here next to my desk) that can be rolled in if I were to want to play an LP or CD/DVD/BluRay, class A/B amp, experience Dirac, hear the (benefits?) of Denafrips DAC w/upgraded PS, or the (amazing?) improvements of a capacitor-riddled power regulating AC filter. But you know that hasn't happened in over a year now. That rack of gear has become an extension of my desk - another horizontal surface to stack papers. 

It's good enough until it isn't. I'm done until I'm not.

One piece of upgraded audio gear is too many and 100 is not enough 

Once you get the room right, size, soundproofing and acoustic treatments, it will be much easier to get over that upgrading equipment need. With an average room, the upgrade equipment bug will never leave you. At least it has been my experience with the house of stereo. Complicated, expensive and lengthy project but I have never regretted it. You get what you pay for is as true as anything in room acoustics.

I’ve spent enough money on upgrades that provided a barely detectable difference (note: not necessarily improvement) despite reviews and recommendations that promised otherwise. So, any future upgrades will be out of shear curiosity or gadget-interest more than an expectation of audio nirvana.