I think there's value. I learned a tiny bit of prolog while looking at semantic technologies, and I found it really interesting. It's an interesting query language for arbitrary data; an alternative to GraphQL that creates "links" by establishing facts about bits of unstructured data.

Is it worth becoming an expert? No. Is it worth spending a day or a week playing with? Most definitely. I have a few niche things I've picked up like that. Learning a little bit of Lisp was similar, although I'd like to learn more of that some day.