Little known languages aren't always actually little known or used, just less and/or not main-stream. They are often languages used in specialized areas or use less common syntax and or structure - like PROLOG and LISP. As such, using them can often help a programmer think and problem solve in new/different ways that may help programming in more common languages. I know learning LISP help my recursion skills.
My LISP and PROLOG skills two are a bit rusty, but I've used (and was proficient with) several dialects of LISP and would probably enjoy a job using either language again.