This painfully speaks to me, though on the hoarding front I was convinced to get rid of certain old stuff and now I honestly regret giving up my old Bondi Blue PM G3 400. But on a more recent note I do still have an original Mac Pro and recently had reason to set it up again with 10.6 Server.
And firing that up and getting back in really hit me like a ton of bricks, yeah there are all sorts of capabilities available now on the newest systems, but the UX there was just so much more pleasant in a number of tiny ways.
You've also said it well, in fact I'd go further and say there was far more then a mere "whiff" of a hopeful future. I looked forward very much to each new release, with concrete useful improvements and the promise of more. In retrospect that was actually the pinnacle of Apple's (genuinely quite decent and promising) server efforts, of a potential alternate world line where they positioned themselves as a strong solution for running things without internet dependencies and subscriptions required. The MP continued to iterate along reliably and nicely until 2010, at which point it died off as a focus at Apple with absolutely agonizing slowness, and with it the dream of a continued upward progression in market support for value oriented hardware capabilities beyond what Apple themselves deigned to offer.
Sigh.