I've pretty much exclusively used mechanical keyboards my entire life. A brief stint where I wasn't using them lead to me having RSI, and I've since switched back and importantly switched to an ergonomic keyboard design. I don't think the comparison to audiophiles is apt (although I'm one of those too, of sorts), because a keyboard is the primary and most critical input device for both work and play when you have your life devoted to computing. I spend 10-12 hours on a computer nearly every single day, the ROI for splashing out $700 for a custom ergonomic mechanical keyboard is immensely better than spending that money doing anything else.
In pure EV/economic sense, spending big on a mechanical keyboard is a fantastic decision if you work/live on a computer.
I'm right there with you on the RSI front. But I do see GP's point on some of the audiophile feel, given the number of people who focus on the acoustics and appearance of their KB.
What KB are you using? I've got a Moonlander that I'm (pardon the pun) over the moon about. The Advantage 360 is very tempting with the curved key wells. So is the glove80. But I would really prefer something that was hot-swapable with curved key wells.
In pure EV/economic sense, spending big on a mechanical keyboard is a fantastic decision if you work/live on a computer.