OP. Have you heard a $20K tubed preamp? I have owned and auditioned dozens of preamps over the last fifty years. They matter, and over time (as the art has developed) and with greater expense they sound much better. Right now I own a Audio Research Reference 6SE ($18K)… after many years owning a ARC 5SE… and it is clearly superior to those before it. At some point I may upgrade to the Reference 10… a two box preamp.
‘’What makes them so expensive? Designing a high end preamp requires a top engineer… but also testing/ knowing the sonic effect of each individual component, how to design circuit boards such that every component and connection avoids interference of everything around it. There are constantly new components on the market… a lot of high end companies end up designing and manufacturing sub components themselves so they have complete control over the end product.
I have had the good fortune to have worked in the high tech electronics industry for forty years. It is truly amazing the value we get for out money. The first high end amp I bought cost $5 in 1979… that is over $18K in todays dollars… my current amp cost $22K…. It is leagues better than that amp from 1979… amps are even an “easier” thing to design.