My dulcimers stay out all of the time
General mountain dulcimer or music discussions
I keep 3 instruments out. As far as humidifying goes, a large pan of water is on our free-standing gas stove (heater) all the time and I fill old coffee mugs with water to keep by the instruments themselves. I know the humidity level in the house is pretty good because I'm not getting snapped with sparks when touching some objects or petting the dogs.
Mark keeps 2 guitars out-- a steel string and a nylon string. Again, I keep a coffee mug with water right by those left out. He rotates his steel string guitars so none of them are out all the time; those in cases are humidified in-case.
As far as dusting them. . . Well, I brush stuff off my instruments from time to time with my hand. :)