OP …”I’m just curious. When you arbitrarily upgrade your system every 7 years, do you hear a significant improvement each time?”

OMG, yes… enormous. Each generation has been such a huge jump. In fact, each component is a very real and substantial improvement.. It can take a year or two for me to do the upgrades. So, for instance I may start by the speakers or preamp… the jump is phenomenal. I spend enough time to get it broken in and appreciate the upgrade in itself before upgrading the next piece.

I a m not sure arbitrarily upgrade is quite right. It tends to be a function of my finances… although very subconscious. I enjoy my system and I think my subconscious keeps track of my finances close enough to tell me when, if I really stretch, I can make a substantial upgrade… which as I am sure you know, for me is to as a minimum double my investment in each component. When I in upgrade mode, virtually every spare minute is reading, evaluating, dropping by audio shops in towns I am flying through… switching into critical listening mode for a lot of the time. 
 

So, when compete, I have a system that is better in no small measure in every respect from its predecessor. I will say I have gotten better and better (yes, partly due to overall improvement of high end audio) at upgrading and the difference has become larger and larger with each upgrade. The last upgrade was definitely the very largest sound quality wise I have ever made. While the investment level was by far the largest, I feel that the ten years of season tickets to the symphony had significantly changed my goals and contributed to the success of this last upgrade. 

How good is good enough?

The answer/answerS aren't so utterly defined by the gear as they are defined by the room, + the actual recording.

Now if I had a room with bang on acoustics that was 18-20ft wide at the front wall and 26-28ft wide at the rear wall. 36-40ft long, with a coffered ceiling 14ft high, then the law of diminishing returns could run hog wild.

One could justify up grading that Denon DL-103R cartridge for a Dynavector TE Kaitora, because in the described environment the expenditure would be clearly audible.

In a room where most of us pee-ons reside (mine is 12x26x8), the above expenditure would be indicative of an individual that has more dollars than sense.

Ya can't make a canon sound good going off in a phone booth, anymore than you can make a pop gun sound impressive going off in a corn field.

How good is good enough? When one has optimized their system to their applicable room!

Enjoy the voyage.

In order to enjoy your system after you’ve found out what’s “good enough” you have to establish that as your base line. After that, you can judge the quality of each recording based on its own merits, and not obsess that any problems are caused by defects in your system. It’s very easy to go down the rabbit hole if you listen for defects instead of listening to the music.

rvpiano OP: That is very true and also applies to most thing in life.  It's all based on personal experiences.  Some are content with a pair of rubber sandals as opposed to going barefooted, while others aren't content with a $1500 pair of shoes.