It's shaped up quite nicely, to my eye. Only the most ham-fisted paintjob could give you a less than attractive (and imposing!) piece of terrain, now.
Airbrushing it shouldn't be a problem - a spray is a spray, after all. Because of that, however, you may want to slather some heavily watered down paint over the sandy potions (I like to mix in a touch of PVA to help lock errant grains down), just to ensure coverage of all those nooks and crannies that can be hard to reach with brush or spray.