Got A Mandolin for Christmas
Adventures with 'other' instruments...
Robin, although I hardly ever play it anymore, I, too,picked up a Kentucky A-style mandolin a few years ago (I also splurged for the one with the solid top, but there is a model without it, so it is not quite the cheapest model) and played it regularly for a while when I shared a house with a guitarist far better than I. That instrument has a very balanced sound, though not as much punch perhaps as the real expensive mandolins.
But I think you are underestimating your abilities when you say there are no crossover skills. That fast and steady right hand you have developed is what's enabling you to jump right in and play some bluegrass chops as part of a rhythm section. Someone without your experience would have to play for a long time to be able to do that. And your general understanding of the music will eventually encourage you to add filler or small solos here and there. You will very soon start translating musical ideas from the dulcimer to the mandolin and eventually vice versa.
You seem to haveconcrete goals with the mandolin and I have no doubt that you will achieve them, but even if you don't take up the mandolin with the same enthusiasm and mastery that characterizes your dulcimer playing, I would bet in the long run, playing the mandolin will make you a better dulcimer player.
And your description of serious practice is a heartening one.

I will definitely check out Custer LaRue's singing.
And I have yet to name my baritone dulcimer, though the lower range might indicate a male voicing. I'm thinking Otis.