"I'm a believer"

This is, of course, nonsense. Most speakers are much better than they seem, you need appropriate source amplification and cabling to make them sing. In any case, so -called law of diminishing returns is subjective, if your hearing is good enough and your wallet is even better $20k for a cable that makes things sound just a touch better is a good move.

This is, of course, nonsense.

Of course the OP point to a real problem here ... And It is not non sense at all..

Most speakers are much better than they seem, you need appropriate source amplification and cabling to make them sing.

Speakers must be not only driven by the right synergetical amplification ,

They must also be embedded mechanically well : vibration resonance control are mandatory ..

They must be also connected to the house/room/system electrical grid , then the control over the signal/noise ratio is mandatory ...

Least but not last thinking that cables will replace acoustic embeddings controls of the coupling speakers/room ,because you even do not mention it, is pure blissfull ignorance ...

In any case, so -called law of diminishing returns is subjective,

Another half truth from you : the diminishing returns TRESHOLD is a ZONE which is subjectively and objectively DETERMINED by acoustics precise concepts and experience and not merely by "taste", it is also determined  by  qualitative design grounded in psycho-acoustic experience not by price tags as the main factor ...

if your hearing is good enough

The hearing must not so well be as "good", it is not enough at all , but trained in ACOUSTICAL experiments in a room ... And musically educated ... We must learn how to hear and what to hear and this has nothing to do with the numbers of audio pieces you will buy and brag about here ...

your wallet is even better $20k for a cable that makes things sound just a touch better is a good move.

This sentence is so preposterous i will only quote it ... 😊

Audio Nirvana at the end of the Yellow Brick Road journey to Audio OZ is a variable reward to different people . This is a well travelled philosophy approach … And yes …achieving it does not have to be tied to an ever-expanding or increasing wallet outlay to attain a like favourable outcome.

I spend three times as much time being entertained on my $5000 “B” system than my $50,000 “A” system. 

Very important post  which must be read by any beginners ... Thanks ...

udio Nirvana at the end of the Yellow Brick Road journey to Audio OZ is a variable reward to different people . This is a well travelled philosophy approach … And yes …achieving it does not have to be tied to an ever-expanding or increasing wallet outlay to attain a like favourable outcome.

I spend three times as much time being entertained on my $5000 “B” system than my $50,000 “A” system.