I'm not sure it's appropriate to consider the money the average human will accept for a micromort as a value that's actually useful for making rational decisions, because that's a value that's badly skewed by irrational biases.

Right. This is why coming up with your own value is a good thing to do. (I didn't talk much about it in the post because it's highly personalized; I didn't want to work through it for all sensible utility functions, and describe how to pick the parameters, and because I didn't want to do it for all of them I didn't want to describe it for just one, because that wouldn't be appropriate for a majority of readers, I suspect.)

Actions are mentally categorized into those the thinker does and doesn't believe (on a subconscious level) to possibly lead to death.

Yep, which can cause people to behave suboptimally. One of the main values of this sort of analysis is it gives you a "risk cost" to put together with a "time cost" and a "gasoline cost." The weekly game night that I drive to costs me $1.40 in risk, $3.20 in gas, and about $6 in time- so the risk is actually a pretty small factor there, but it could tip the scales for marginal activity. (You do need to look up the mortality numbers- which can have a non-trivial cost- but doing research when it's worth it is a part of careful decision making.)

The end result of everything I just said is that the "value" being assigned to a micromort is probably more a reflection of how the EPA ran their test than what people really value; they'd get a different result evaluating people's aversion to micromorts via car crash and people's aversion to micromorts via being mugged

I'm not sure how the EPA runs their numbers, but the way I got mine was by calculating the value of my life (on the margin). I think people can give reasonable answers for things like "how much longer would your life have to be to compensate you for a 5% decrease in consumption?", which is less subject to biases than visualizing particular causes of death.