Ugrade-itis - is there a cure?

There is no cure I am aware of, nor should there be. When you are done you are already "six feet under", in a manner of speaking.
As for the expenses, many other things are just as or more expensive. The trick is to be able to keep it under control, this doesn't mean stop.
I keep hunting for best pressings too.

I am very fortunate in that I am entirely satisfied with my system which incidentally has seen no changes since 2015 aside from a repair and software update. I have no plans to change components and figure that one day I’ll have to replace my decade plus old phono cartridge. These days the $ I spend on this hobby is all devoted to getting more music. To me, reaching that point means you’ve made it! And I have. 

Ugrade-itis - is there a cure? 

Sure. Until the second system could sound a little bit better if I only.........

It’s a hobby. There is no perfect system. I find that new stuff makes my records sound new again. And really I have audio stuff to listen to music, so if new stuff reinvigorates music I enjoy, it’s a huge win. The new stuff is not necessarily better, it’s just different. I like vintage audio these days so I have a parameter of sound I am going for.  The only reason to stop (other then money of course) is that you’re no longer curious. It happens. 

And as hobbyists, I think there’s always an interest in tinkering, improving, etc.
What helped me was shifting my focus to the records (or whatever your preferred medium is). Lots to learn, lots of music to get played that’s new and different to you and a huge amount of history to the recordings, the artists, etc. You can get all geeky on pressings if you like to improve sonics more.
But, it isn’t just something to keep me busy.
It’s the food for the machinery. And into the maw it goes. Some stuff gets put on a shelf and forgotten (yeah, I do purges every once in a great while) and some stuff becomes part of me.
After all, that’s what we’re chasing this good sound for, right?
It will definitely keep you off the street, and probably help appease those "I need something new/different" blues. Ain't no cure.