I was just perusing Steve Horwitz's JEBO article again, which I hadn't read since I got the special issue from Peter Boettke in a little Coordination Problem contest. I was reading it before more in the context of my own interest in James Buchanan's constitutional work than in the context of the rules vs. discretion debate, so I hadn't really taken notice before of this article from 1936 by Henry Simons on the same question (it's called "Rules vs. Authorities in Monetary Policy").
The discussion does go back quite a ways!
I have a lot on my plate... probably won't be high on my reading list. But I thought you all might be interested in it.