So other than nostalgia, loyalty, or curiosity I don't see a reason to get a new mini if/when one comes out.
Well, you're only going to get "anecdotal" evidence for this...
I probably won't be buying one this year, because, a bit over a year ago, I reluctantly decided to get an iMac after it
narrowly won an "is it time to give up and switch to Windows/Linux?" debate. I'd have preferred a headless system - but not
quite enough to give up MacOS. However, its quite likely to be my last Mac unless Apple starts offering a wider choice of systems. In a couple of years' time, though, a "pro focussed" mini (as rumored) or (unlikely) a "cheesegrater redux" Mac Pro might well tempt me - unless, of course, the computing world has changed beyond recognition by then - but it hasn't really in the last 5 years or so.
Then there are a lot of people still rocking old machine because they don't like the modern alternatives. Reality is, anything made much after 2010 is still a viable option for many applications - especially since the current Mini is so old (and actually worse than the 2012 model in some ways).
However, its the "pro" field where your question really comes in to play - especially businesses that lease their computers (or write them off against tax on a 3-4 year cycle) and, unlike "enthusiasts", will feel compelled to replace them once they can't get service cover. I don't see who is going to buy a Mac Pro 5-6 years after the last one was released and still with no
real indication of what is going to be released and when.