I have no evidence for any of it except the anecdotal mumblings of an old man ;) Though a lot of different societies came up with 12-based systems, so there might be something to it.

It is clear that illiterate people could work in "old money" fine. I suspect this is like the darts players who can do the mental arithmetic involved in a darts match fine, but would consider themselves "bad at maths". It's a learning cliff, but like any learning cliff, it no longer matters once you've climbed it.