Wouldn't it also mean that we should treat "perfectly correlated" as isomorphic to "uncorrelated + dictator filter", since you always believe your vote determined the outcome?

Not ahead of time - you know, ahead of time, that your vote has only one chance in N of determining the result (if you want, drop the "rewriting people's memories" part of the dictator filter; it's not really needed).

By the way, how would your application of CDP/SIA to the Absent-minded Driver problem take into account additional evidence fed to you about what intersection you're at?

Let me think about that for a bit.