I've read parts of two of Holschlag's books on fishing for smallmouth ("Stream Smallmouth Fishing" and "Fly Fishing for Smallmouth") and I've spoken to him (once), and I think that he favors a kind of "impressionism" when it comes to tying smallmouth flies. So I'd say that I've benefitted from his expertise, and I agree that tying crayfish flies so they have the right movement in the water makes a lot of sense.
Just a suggestion. In the last chapter of his book "Good Flies", John Gierach discusses a pattern he calls the "Mud Bug" (a fly that resembles Clouser's Foxee Red minnow) that he based on his experience of watching crawdads' behavior. He came to this conclusion when it comes to crayfish flies: "I got to watching crawdads in trout lakes and decided that most patterns were way more detailed than they had to be to catch fish, and possibly too visible, as well." I take this to mean that, not only must a fly have the right movement, it must have the right (i.e. muted) color as well.