I don't mean to be hyper-defensive or anything, it's just that it was kind of an insult to me personally. In my studying of noise abatement, I've checked several references and read posts from several different people who study acoustics and have in field experience no less credible than yourself; and I am pretty good at inferring from data, as I was a college student for a few years, studying a variety of topics. Ultimately the conclusions I've drawn from all the info, posts, and acoustical data are concurrent with what real live experience I have gained in soundproofing my bedroom. Honestly, I don't want to come off like a know-it-all, I was just freaking curious; I just figured it would be convenient to show the info that I had recently read about it.
That being said, one style of insulating that has gathered more attention in recent years is the idea of insulating with only rigid insulation, with the stud bays and rafters being open (no cotton, rockwool, or cellulose here) and only used for support; the fact that all the insulation is clad over the framework nullifies any heat coupling effect of the framework.
As the several inches of insulation would have siding or plaster covering it, one can't help but wonder how well such a structure would compare to a double wall in sound deadening, especially if expanded cork is used (it would have to be better than the poly right?).
The article mentions that gathering the cork is somewhat labor intensive; just the same though, there is potential for industrialization, not to mention breeding varieties of this tree that can be grown in different climates. I just figure it's worth a look into.