Art, it has always been my theory that Joseph kept his guitar out of tune and certainly not in concert 440 on purpose - a kind of musical joke for the listener, almost like he was saying, "Look how good I can make this cheap guitar sound even when it isn't in tune." His music is so heartfelt and whimsical at the same time, and, yes, his singing is definitely part of it even though it is a pain in the ass to listen to at first.
The Rolling Sea CD Jim Dixon mentioned has some great cuts on it. Others seem like they were trying to adopt Joseph's style of making the music "hard to hear." I guess I better give them a few more listens. Out of all the cuts, I always thought the otherwise unrecorded Japheth Dean captured Joseph's style the best.