Thing is, it looks like your generalizations are based on umm, "thought experiments'.
So lets break this down a bit. It seems to me everyone will fall into one of these camps, or perhaps inbetween two of them.
You're right, there are two camps - those who just talk, and those who have actually done their homework. In case that seems overly general, by that I mean actually done level-matched, time-synched, bias-controlled listening tests of amps.
1) No matter the price, all decently built amps sound about the same,
That is observable reality.
2) While there are small differences between so called "high end" amps and your generic consumer electronics, the differences are too small to merit the exorbitant costs associated with the really pricy equipment.
Who cares about that when reality is: No audible difference.
3) Between say $100 receivers and $1000 power / pre amps, there is a pretty substantial difference, but after that, their is a steep curve of diminishing returns.
No, between $100 receivers and $100,000 power amps that measure at least as well as a $100 receiver (many don't) there is simply no audible difference.
4) At every price level, there are noticeable differences.
That would be known as the "fantasy" position.
The facts automatically preclude your remaining position since if the above is false, so is it..
To keep this friendly, just provide one example of an exception that we can check out...