Your second paragraph seems to point at the mystery of subjective anticipation, aka probability. I had some ideas about that, but no conclusive answer. It does seem to be a very confusing problem.
the importance of relative causal significance
Please explain this phrase?
We haven't discussed it here yet, have we? Article from August 2010. ArXiv link. The upshot:
The notion that I am this huge equivalence class of almost-identical human beings (just similar enough to be running the same mind-computation at this moment), scattered over a spatially infinite universe, sounds very UDT-ish. Unfortunately I don't know enough physics to judge the paper properly. Please halp.