As you might gather from that, it's not clear to me that you can include an "observer" in this sense as part of the overall wavefunction of the universe at all,

As you might gather from that, it's not clear to me that you can include an "observer" in this sense as part of the overall wavefunction of the universe at all, though perhaps people who have studied the foundations of quantum mechanics in more detail could give a better answer. I did some more reading and it seems that at least some try to do what I also considered, try to attribute the randomness in the outcome to the randomness and uncertainty in the initial state of the measuring device, observer, and environment. This then raises the question why all kinds of measuring devices produce the same distribution of measurement results if the concrete outcome essentially only depends on the initial state of the measuring device. And this also has the smell of a hidden variable theory where the hidden variables are in the measurement device, would this be compatible with EPR? I also took away some things to follow up on from your comments on Everett but unlike you I don't really like multiverses and so this will have to wait for some time. I however agree that Everett makes the most sense with regard to completeness and consistency.