Matt,
A very good, soft brush I use with good results is a makeup "dusting" brush used by women, and available at chain stores or anywhere that sells makeup and supplies. If I recall they may also come in a couple different sizes.
I got "turned on" to this item when I was working at a local TV station a few years back. The engineer at the station had his assistant use one of these now and then to dust off the face of various pieces of electronic equipment. Worked like a charm and didn't move any knobs, sliders, etc. from their settings. It simply went around these things and just removed the dust. On your models it is the friendliest way I've found to dust around a model's delicate details without breaking them off. I've since been using one to also dust my electronic equipment at home, the glass on my lighted magnifier and my models.
Many times I have needed to dust something delicate around the house or even the front dashboard controls and heater/fresh air vents in the car, and the "girlie" brush always shines.
"Paul - The CB&Q Guy" (Modeling 1960's In HO.)