"I'm a believer"

There is definitely a Rule of Diminishing return just as there is the Sunk Cost Fallacy. I suspect that the Venn diagram of those two circles would be close to one circle in some cases for certain audiophiles. For example, someone subconsciously suffering from the Sunk Cost Fallacy has spent years and enormous amounts of money in their pursuit of perfection and yet never attain it as perfection does not exist. So each subsequent purchase is rationalized as moving closer to audio perfection. Yet the reality is they would not / could not admit - even with hard facts -  that the recently purchased $100K speakers are marginally better or equal to the $10K speakers or even the $5K speakers because they suffer from the Sunk Cost Fallacy. The diminishing returns set in long ago for each dollar spent.

The Rule of Diminishing Return applies to many industries where the marginal performance gains do not justify the cost, yet at the high-end market of consumable goods, the real reason is justification for many that they can exhibit how they can "afford" to pay $150K for certain speakers, or $200K for a vintage Jaguar, or any luxury item for that matter. Some may actually know they're getting no real qualitative improvement for their investment because the point is to exhibit their wealth. 

@waytoomuchstuff I agree with what you're saying but I think there are actual qualitative steps in manufacturing quality across many sectors including audio components and speakers, but the ceiling price point where diminishing return sets in, in my experience, is probably the upper-end of the mid-range components available these days. After that, you're entering the luxury end where people (IMO) are paying to display the item more so than having the expectation of a huge jump in performance.

For example, my vintage Craftsman tools are of better quality than the new Lowe's Craftsman tools purchased for about the same price (adjusted for inflation) but only because I think they are. My Wera sockets and torque wrenches are better quality than the comparable Park Tools and the price point shows it but only because I know what to look for quality wise. If I hand a hex wrench made by Wera or Husky to my wife so she can tighten a 5mm bolt on some cabinet she wouldn't care to know which one was "better" as either one gets the job done.

I know when I spend my money on certain things I focus on getting the best quality for my $ knowing I have a ceiling to that quality for the $.

@mahgister Oh I agree on the acoustics of the space probably being one of the most important factors in getting the acoustical characteristics you're hoping for out of the components and speakers you have. I know that if I went out and spent $5K or $10K on speakers for my set-up, it wouldn't be a wise investment. My listening room is an open-plan living room/kitchen with high ceilings and off-center listening positions. I can't acoustically treat the room. As it it, my wife complains about the stand-mounted bookshelves I have now.

We're planning out our forever house and my man cave will be a listening room/library with a drawing/writing desk and 2 comfortable lounge chairs. That room will be acoustically treated and dialed in and I will probably plan on spending $3K at the most for a final set of speakers. My current set of speakers is fine for the space they're in since I primarily use headphones for critical listening and the bookshelves are used for background listening coupled w/ wireless speakers in other parts of the house.