Good to see you Scott- although I guess it's only been a few days
I understand the issue with the dullcoat spray. I don't know how much of that dry, dusty look it would get rid of, I'm never sure what to do or how much of a coat to give it. One idea you might want to try Tom, would be an artistic pastel fixative (I don't know if it's that much different than a dullcoat, so maybe just check out the can and see what it's made up of) but it'd be clear and designed to fix pastels to paper/canvas/etc. Again, don't know if it's specially formulated or if it's the same thing that makes up a clear coat spray with a different name...
As far as how to get the look prior to the fixative, good luck!! hahah I think you should ask Will, he's had better results than I- I like the make up brush idea, but I think that would give it an equal, even coat of fine dust- I liked the look Will got with small clumps, fine dust- some cleaner and dirtier areas. He probably just used a small to medium sized paint brush. But that's just a guess.
Looking forward to seeing you revitalize this one Tom!