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.