Wow great post.

I've been thinking about this too. I haven't liked clay bricks or straw/clay, or adobe or rammed earth for us here in the NW because low R value and maybe not so good in the rain (not to mention earthquakes). However, in keeping with my desire to use local materials, I've been thinking about pumice. There is a lot of this red pumice mined around here for gravel roads. It's full of air, it's light weight, combine it with cement and you have a strong light weight warm wall, yes? I believe there is a man in NM doing something like this:

http://www.pumicecrete.com/Hybrid-Building-Applications.htm