Affordable vs. ultra expensive speakers - what's the difference?

Having owned $2,500, $5K, $12K, and $34K speakers I assure you performance jumps are the primary reason to purchase ever increasingly expensive speakers. While cabinetry costs increase they most get priced for perform. The diminishing returns argument doesn’t really work until you get way up in expense because audio systems are like instruments, they get more sensitive as they get better and as such get more compelling to listen to. 

There are certainly differences, in every aspect of sound quality. 

But if one is expecting the differences to have some sort of 1:1 (for every $ more I spend, I will get exactly that much more improvement) correlation, that will not happen. 

The higher up the scale one gets, the less the improvements will get. A $50K speaker, will not sound twice as good as a $25K speaker. But, it will probably sound quite  bit better than the $25K speaker, than a $100K speaker will over a $50K speaker.

That being said, the difference the YG Hailey will have over the Monitor Audio, will be appreciable. I have heard the YG's plenty of times, and I have heard Monitor Audio before (not the ones in the link), so, I am speaking from pretty good experience. But, pretty much all aspects of preproduction will be better with the YG.

i think it is worth clarifying one important point

diminishing returns does not mean lack of or negative returns

it means as you spend more tranches of the same amount of money (call it $1000 each time), you get a declining degree of positive benefit (in this case, better sound) for each additional $1000 spent - but you still DO GET MORE benefit

said another way, in a world of diminishing returns, so long as it is spent with proper knowledge and insight in the aim to improve, spending more gets you more of what you want

and thus, the controlling idea here is more about how many more $1000 you are willing and able to spend, versus whether those additional thousands will get you further in your pursuit of what you desire...

Yeah, with regards to audio, I really don’t believe there is an objective point of diminishing returns.

It is up to each individual to decide where that point is for each of us.

My rich cousin recently upgraded his previous speakers, Magico M3 ($80K), to the a pair of Von Schweikert Ultra 9 at $200,000.

They sounded slightly better in almost every aspect, and all those slight differences added up to a more compelling, involving listening experience. Was it worth the more than double the price for those small improvements? It was for my cousin.

And let me add, that the vast majority of music listeners out there, listen to MP3s on $20 dollar ear buds, with their smart phones, who think that those here who have only spent a few grand on their modest systems, have surpassed the point of diminishing returns.