I think it is quite prevalent. Audiophiles are often hoping for minute changes with the addition of often expensive upgrades. This is a dangerous combination for objective determinations; we will often think we hear what we want to hear.
You are exhibiting the typical naysayer (fake) suspicion that these tweaks cannot have more than a miniscule effect. Buddha would undoubtedly approve your using his "mote of dust" argument. Mumbo and more jumbo.
Additionally, changes made by a product are often described by both the press and individual enthusiasts as "astonishing," "amazing." Those that come next expect to hear at least "something," even if it is not "astounding."
Sorry to hear you've had such limited success and experience with tweaks. Color me shocked.
No one wants to be the person with deficient ears and equipment that hears no change even after the "amazing" product is added.
It's a lousy job but someone has to do it. Are you volunteering?
Sadly, those that push such products often claim that those that do not experience an improvement are personally deficient, close-minded, and possess inadequate equipment to appreciate the finer aspects of music reproduction. We have witnessed these personal attacks often in these threads.
You forgot to include those that never try these tweaks - they won't experience an improvement, either. It's apparently more fun being a troll. If by personally deficient you mean their hearing skills are undeveloped and/or they're all thumbs when it comes to assembling an audio system, I concur. But if you mean they have some sort of worrisome psychological issue, that will take some more digging. I'll get back to you.