It's not that there never was anything worth learning from theists, it's just that by this point, everything of value has already been inherited by our intellectual tradition (from the time when everyone was a theist) and is now available in a suitably processed, relevant, non-theistic form. The juice has already been squeezed.

A word of caution to those who would dispute this: keep in mind the difference between primary and secondary sources.

As an example, the first is Mein Kampf if read to learn about what caused WWII, the second is Mein Kampf if read to learn about the history of the Aryan people. The distinction is important if someone asks whether or not reading it "has value".

That said, zero is a suspiciously low number.