An unstaffed halt on the existing line between Glasgow and Dumfries (and Carlisle) would be a relatively modest investment for the community. There would be minimal infrastructure work (looking
here, the platforms were actually in decent shape back in 2009).
The numbers aren't great, granted. It is well situated as a park and ride for nearby villages as well, but they won't add all that much to the numbers. But let's remember that the line is already operating and the bulk of the infrastructure is there. It would be a relatively modest investment that could really benefit the community.
Services to Glasgow and Kilmarnock are already in place, so that's all fine and dandy.
If it's going to be of benefit though, there do need to be trains getting into Dumfries for commuters (all 200 of them). The first arrival from the North into the town arrives at 09:00 - too late to be of use to commuters.
An earlier train can be had by taking the current 07:43 Dumfries to Newcastle and turning it back somewhere further North (also providing a commuter train to Carlisle). The timings would work nicely to take the Carlisle-Dumfries service that forms this train and running it up to Sanquhar rather than sitting in Dumfries Yard for quite a while. The train is productive in the time that would be spent idling in a siding. But that would (I think) need more infrastructure work which does come at additional cost. Still, you'd also be wanting a train getting into Dumfries about 45 minutes later, which might mean retiming the morning Glasgow-Carlisle train a bit to get it in earlier than 9 or getting another unit.
You'd also need Northbound trains leaving in the evening peak. There are none in the current timetable. 15:50 is useful for some but too early for most. 18:35 is useful for some, but too late for many. You'd need another train at about 17:30. And that would probably need another unit.
A better solution could come if there is an hourly service on the line. This would make the new station even more attractive and hopefully the recast timetable would see more trains arriving into Dumfries in the rush hour. And it would boost the existing stations too.
So there's quite a bit more needed if this is going to be viable. The station itself comes at a cost, but the additional infrastructure and additional unit(s) needed would push that up somewhat. But it would be a great addition to the community, and I'd like to see this come to fruition.