Inners/Glentress is already fairly well catered for but will be the highest demand by far. Probably less non-bikey outdoorsy. Some of the existing places like Glentrail have shut (I heard Chris Ball’s place is shut too, anyone know?)
I can’t think of any places down in D&G that promote themselves as really bikey- maybe I’m just oblivious though. The trails are much more spread out obviously and I don’t think any of the decent size towns have much of a draw so maybe harder to pick your location? But Dalbeattie and Mabie are pretty close together and reasonably central for KT, Ae and Drum. (we stayed at Kippford last time- I’d never thought of that before but it’s near perfect, ride to Dalbeattie, quick drive to Mabie, Kirroughtree no more or less of a pain in the arse to get to than it always is)