It's a geek badge of honor. I own a few and I love them like my children (okay not really, maybe like my pets) but part of that comes from the effort I put in to scrounge them and clean them up myself. I do like the feel of typing on a Model M but what I love is the feeling of gravitas (figuratively and literally, it's really heavy).
Vintage hardware is neat but most of it is of no practical use today. Is there any other part of a 20-year-old computer that you could still use for day-to-day tasks? A Model M lets you feel old-school without actually having to live in the bad old days of floppy disks and 300 baud modems.
I type on my wife's Mac keyboard and it's fine. I type on a rubber dome keyboard at work and it does the job too. Maybe I would feel differently if my job required pumping out hundreds of thousands of words very quickly, but for most people (and, I suspect, most Model M owners) that's not the case.
Nostalgia is fun. It's okay to have a "throwback" keyboard if that's what you want. Not every technological choice we make has to be justified by greater efficiency or superior ergonomics. Relax and feel the Model M love.