What is your experience with the law of diminishing returns ?

Cables and power cords are components and as such they can sometimes give as much sound change as active components.
However, speakers might not be good enough, so whatever you replace in the chain give about the same magnitude of change.
Or, your system is a total mess, completely in disarray, and whatever you do it won't matter much - same mess.

I think that Elizabeth has it right in terms of marginal cost / marginal gain curve.   One might quibble about price point (not a lot).

Then the owner’s financial condition as well as sensitivity to the curve must be factored in.

For myself, I lust after the new 30.7 Maggie’s, but a house downsizing leaves me a room 23 x14, not quite large enough. At the end of the day, I love where I am I terms of my system, but we always see the greener grass smiling at us, LOL.

Also, often lost are the relatively inexpensive tweaks, I.e. room treatments, etc.

Reminds me of the old line, "What's the difference between a $2.00 cigar and a $10.00 cigar?"  Answer:  "$8.00"

One knows then the good old diminishing returns (more money than sense is a better term) has truly set in when one's stereo is to good for Redbook CD's........haha