Is positive reinforcement why things are sounding better?

Recency Bias is a real and enjoyable thing. It is tested by how long the effect lasts. Good luck!

Acoustics parameters must be improved all together and put in balance for a specific ears/brain...

If we dont learn about all acoustics aspects of sound it is easier to loose sight of one...

But sometimes we forget this because of our focus bias pick one thing that matter for us and let the other aspect aside :

Remember it's a hobby.  Don't spend more than you can afford or money you will regret spending.  I've made many "upgrades" over the years.  I would say 70% have been an improvements and the other "upgrades" I have sold over time.  I often buy used and when I resell and consider my cost often and the entertainment I've gotten, it's in range of hobby expense.  I'm a liitle surprised about one thing:  when i upgraded an amp recently I gained bass control, elimated fatigue and etchiness and gained bottomless reserve.  I lost some imaging and defintely speed and quickness. For me some upgrades have just been clearly superior, but as I've gotten better equipment the upgrading has usually resulted in more nuanced improvements.  

@immatthewj 

Confirmation biases has nothing to do with "lying to ourself" in particular or specifically

Yes, it does, obviously.

Careful, @hilde45  , you are heading down the road to crazy-town. 

Don't worry. I have enough to do in life than quibble on the internet. Those who know how to understand English will take my meaning and either agree or disagree, coherently. I just ignore those (bots?) who make random, semi-literate grunts. Saves my time.

I just ignore those (bots?) who make random, semi-literate grunts. Saves my time.

Good plan.