It seems to me that "diminishing returns" has a pretty straightforward meaning, that as you spend more the incremental improvement per dollar becomes less and less.
With that as a working definition, I've owned or at least used scopes from cheap ones to very high end. I think that in new scopes the Burris FFII represents a good, reliable and effective choice for hunting, and I own three of them. Cheaper scopes than this have not proved to do the job for me, so the return for dollar spent on them has been effectively zero.
Spending more than the Burris FFII can give improvements in some areas, but it seems to me I'm getting less and less for each additional dollar. I would rate the Meoptas I own or have used above the Burris for example, the various German scopes higher still, but there's definitely less and less improvement per dollar, so IMHO the price point beyond which I see diminishing returns is at about the level of the Burris.
A quite separate and different question is "how much do I need to spend to get a scope which is good enough" , and the answer to that will depend on what you want it for. Whether, for example, you want it to dial repeatedly, or to use it in very low light. How critical you are too, of things like colour rendition or the quality at the edge of the field, and perhaps how good your eyesight is. How rugged the scope has to be too. Perhaps pride of ownership too.
I personally have been happy with medium-priced scopes, for what I use them for, though I have several European-made ones and have used others. I have a mate who won't be happy with anything short of "alpha" glass. Each of us is free to choose what we like.
