I think this hobby if full of opportunities to experience diminishing returns. However, there is a difference in sound quality. If you buy a pair of $15,000 speakers you then have to spend half that amount on an amplifier to drive them.
It would be fun to take a survey on how much people are worth who spend $100,000 on their system. It would also be interesting to find out what they do for a living. Perhaps, this would cause people to seek a profession that can support that level of spending. I also think people in this hobby are obsessive compulsive. Are they people who are typically negative who will never find a way to be satisfied. I also have seen pictures of some of these expensive systems. I know my wife would not tolerate the appearance or the spending.