Well.. I sort of agree.
I agree in the sense that if you get a summit-fi performing pair of headphones for a mid-fi price, you've gotten fantastic value. But I don't agree that this is an argument for why mid-fi is where the value is at (since you can find "bargains" at essentially any price point), nor do I agree with the notion that mid-fi can be called "value" at all.
Someone on this forum has a really nice quote which is something like "audio is all subtle changes and none of it is worth it". It basically just sums it all up. The truth is that for any normal, non obsessed human being, the changes between headphones are so laughably subtle and CERTAINTLY not worth hundreds of dollars - so talking about value in terms of headphones worth more than 50$ is a bit silly imo - most entry level headphones gives you the most vital information on a track. Now, for us obsessed people.. There are different tiers I guess. Some think entry level to mid fi is the biggest jump in quality. Others, like me for instance, felt the jump from mid fi to summit fi was biggest. In terms of real world differences for the non obsessed, we are both wrong. In terms of difference for our own ears, we are both right.
So I think that talking about "value" and "point of diminishing returns" is a bit silly. Okay, if I start spending thousands of dollars on usb cables I'm probably well beyond the point of dimishing returns - but as long as we are talking about headphones, such a thing doesn't really exist. This is head fi, so I trust most people here understand that its stupid trying to quantify quality changes by looking at FR graphs or dumb stuff like that when talking about AUDIO. What we do know is that there exist "reasonably" priced equipment that gets everything on the recording delivered to you in a spectacular soundstage (HD800), and which we can easily call the "technical pinnacle". But audio enjoyment or the quality of audio reproduction doesn't work like this at all. I'm not saying that the sunken cost fallacy etc isn't a major factor in a lot of peoples opinions when it comes to audio, but what I'm saying is, value is a bit silly of a term when it comes to audio. If that makes sense.