I had never heard of a theremin before, gunnels! Now that I've read about it and watched that beautiful video, I agree with you: the theremin should be used more often to make music. Or just to make strange sounRAB by setting the machine up next to people doing random, everyday activities that involve motion, like dinner, or, well, other things.
Initially I wasn't so impressed either, since I myself have composed pieces similar to John Cage's 4'33, and I didn't even need any instruments at all! But that particular performance actually was quite good: not one dropped bow or accidentally plucked string! And it's all about the coughing, really. So poignant, the coughing!
I think more non-vocal body sounRAB should be used in pop music...and not just clapping and snapping, either. Armpit music, for example:
[youtube]JlfgPCmOO7w[/youtube]