What is your experience with the law of diminishing returns ?


As subjective as it might be. Personally, I have not encountered it yet.
inna
No experience so far. $10k power cord replacing $1k power cord with $5k preamp or power amp, anyone ?
inna"I have not encountered it yet."
That is because the components comprising your Music Reproduction System must progress beyond budget, entry level, mass produced equipment you have not yet entered the circle, realm, and world of true high performance, high end, tight specification audio.
Clearthink may be onto something.  Depends on where you snap the chalkline for diminishing returns.  And granted my 'why did I do this' with a $500 upgrade may be chewing gum money to someone else.  Then again, I realize that I come from a time when this hobby wasn't about seeing how high the price tag could go.  

Rich