Thanks for the comment, Paul -- really appreciated (as are the other comments in this thread) and very helpful.
I suppose I'm contemplating a 'best compromise'! I'm getting on (58) and have advancing osteoarthritis in my spine, so need a 'softish' riding bike. My 'roadified' hardtail mtb works well enough, but it probably errs on the side of 'off-road' more than I really need, and I'm getting tired of the on-road inefficiency of suspension etc.
On the other hand, I still think I'm 25, and have always dreamt of long-distance on/off-road touring, and like to think I do and can ride quickly, even though I probably don't in relative terms! So, I'm conflicted!
Realistically, I'm looking for a bike (I'm a 'one, good bike' sort of person) that I can use February/March through November/December on a daily basis, but which could with a few quick mods. be used for, say, an extended trip (Route Vert) up along the St Lawrence and into/even through the Gaspe -- that kind of thing. I'm in Ontario, but we have a summer place on the Fundy coast in NB, so lots of opportunities for good riding.