"A primary reason I don't always update when people disagree with me, is that I don't think they're taking that disagreement with the extraordinary gravity that would be required, on both sides, for two people to trust each other in an Aumann cage match."

The problem with this is that there is at least a small probability that they are taking it with that gravity. Given this small probability, it is still necessary to update, although a smaller amount. This was my point in the previous post. The fact that you should update when you are surprised by someone's opinion doesn't depend on Aumann's theorem: it simply follows from Bayes's rule, if you accept that there is at least some tiny chance that he holds his opinion for good reasons, and therefore that there is at least some tiny chance that the truth is the cause of his opinion. For if there is, then the probability that he would state that opinion, given that it is true, is greater than the probability that he would state the opinion, given that it is false. Therefore you should update your opinion, allowing his opinion to be more likely to be true than you previously thought it.