The law of diminshing returns?

You are right for sure about linearity ... but you forgot the objective and subjective acoustics conditions necessary to the evaluation of the price/ratio/ performance of the gear ...

 i said objective because system/room/ears/brain imply objective parameters but also subjective non measurable parameters linked to our own personal journey and acoustical maturity...

Then the relation is non linear ...

To the OP's point about "diminishing returns", I would consider the relationship between money spent and performance gained to be much more logarithmic than linear. 

 @newton_john  The most recent addition to my system cost $300 (two sets of 8 lifters) from Target (sold everywhere).  I went from 1.5" high rubber 1980s footer/pucks under my speaker and power cord cabling lifters to 6" high Audioquest Fog Lifters.  The difference in sound quality was in my estimation at least $10,000 worth.  Sometimes the smaller changes can be the most dramatic.  My problem was not vibration as my room has very thick plush carpeting on 12" thick 3000 psi reinforced steel concrete slab.  It was the proximity to the supposed "non-static" carpeting.  6" above the carpet worked!!!

It wasn’t quite like going from Blue Jeans/Belden XLR cables to Westminster Labs Ultra XLRs but maybe half that.  For lower resolution systems, I don’t know if the difference can be heard.  

@kevn I absolutely need a network for streaming, my setup uses two streamers and a separate remote device. I have two routers, audio system only router is Netgear XR1000, both modem and router operate on 12v, my lps are buried behind much equipment so hard to access to give you exact Terakak model. In any case both not switchable voltage, modem LPS about size of the one you referred to, router lps much larger, router requires more amperage.

@sns - thanks for your kind and detailed replies - best if I take this off the thread, I’ll make response in your system page if you don’t mind : ) 

In friendship - kevin

I think of it in reverse.

i love my (fairly expensive) sound system, but i can also enjoy a good song on the AM radio in my car with the windows open.