The law of diminshing returns?

@newton_john, No evidence whatsoever.  It's just an opinion.  Feel free to agree/disagree.

The extreme budget minded Audiophile will always view this hobby as "The Glass Is Half Empty". This validates his skewed anger/fear regarding anything in this hobby that is outside his comfort zone.

"The sonic difference may be subtle or even negligible, but the ownership experience, physical presence, and perceived exclusivity are the real “product.”"

The above statement is the opinion/bias of the author of the article linked by the OP.  It is important to remember that all audio reviews, forum postings, and manufacturer advertisements are biased by the experiences, personal preferences, and goals/motives of the author.  I found it interesting that the author began his summary by listing multiple reasons a more expensive DAC might sound better, including improvements in:

• resistance to vibrations/micro-vibrations,
• resistance to EMI,
• power delivery,
• signal clocking,
• digital conversion,
• output stage,
• thermal drift, and
• channel separation,

and yet, the author's conclusion was that all of these improvements result in only "marginal performance gains."

After many DAC upgrades, and some sideways moves, my experience has been that while paying a higher price is not a guarantee of better performance, in most cases, the higher priced DACs offered some combination of a more realistic tone, improved clarity, a lower incidence of the digital artifacts that detract from listening (i.e., they sound more natural, organic, and/or analog-like), and improved dynamics.  These improvements result from the very design/materials/construction improvements identified as typical for higher priced DACs by the article's author. 

My most recent DAC upgrade, from a very nice sounding Mojo Audio DAC, to an Aries Cerat Helene (at about twice the price) included most of the  design/construction/performance improvements listed in the article, as well as a tube-rectified power stage, and a tubed output stage.  In my system and to my ears, the more expensive DAC brought the sonic improvements I listed above and resulted in an even more natural sounding musical presentation.  Whether some would call that a "marginal" or "subtle" improvement or something more is personal opinion.  The more expensive DAC certainly doesn't offer twice the level of measured or subjective performance, but it does offer a meaningful and valuable improvement in that, in the context of my system, experience, listening goals, and budget, the value is certainly noticeable and worth the additional cost.

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.  IOW, the further you get from the origin (i.e., the more you spend) the smaller the sonic improvements/gains per dollar spent.  However, whether those gains are meaningful and valuable compared to the cost can only be judged by the end user.

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.