just the fact that the word 'subjective' has been used in many of the responses is but one way that ones ego can influence. trying to out-do the next person buy spending more, not necessarily achieving 'better' yet satisfying your ego. Our egos are fed and satisfied in different ways .......
This thread is limiting returns to money. The return from a high end audio system is primarily intangible.
But yes, hifi and nearly everything else in the world has diminishing returns.
I have sex with the most beautiful woman in the world. The first time is more rewarding than the 1000th.