This is the most ridiculous discussion/theory I've seen in a long time. The law of diminishing returns is a proven theory of economics time and time again. Anyone who thinks an upgrade from a $5K amp to a $10K amp improves SQ LESS than an upgrade from a $50K amp to a $55K amp is nuts. Maybe it works from a % spent upgrade standpoint, but I even would question that. And if it is breakeven, it still is not accelerating. The graph submitted above is on the money, but of course there are different inflection points.
I think it is great to experience all stereo possibilities, especially within the specially designed rooms, and if you want to spend the $$ to enjoy them, but please do not try to cost justify them as being of incremental SQ improvements. Value on the other hand, is in the eye of the consumer. If someone is willing to pay double for a very small improvement, then he/she sees the value, and more power to them. Some see the value in how it looks.
Some see it as a luxury item like a Rolex, but I would think most Rolex owners think of them as investments that go up in value whereas stereo equipment rarely does, and I would hope nobody goes into the hobby trying to make money (unless they are a dealer) when buying equipment.