Is it as low as it was?

I'm not sure. People in 1900 or 1950 had less knowledge than we do now, but they might have had a mainstream culture that took the knowledge they had more seriously than ours does. I'd have to be more of a historian to be able to tell how much this was actually the case.

How well does having Jaynes, Kahneman & Tversky, and The MIT Encyclopedia of the Cognitive Sciences measure up to creationism as a political platform, blank-slate leftism and postmodernism in academia, or climate denial and anti-vaccinationists getting massive media attention?

EDIT: My mental model of Robin Hanson also notes that all else being equal, you might expect people with less surplus resources to have a higher sanity waterline, since they have a smaller margin for engaging in delusional signaling before they start running out of vital resources like food.