I would say that learning Lisp is definitely worthwhile and will improve your Python coding; pg's essay argues for Lisp better than I could:

http://www.paulgraham.com/avg.html

You'll want to not just read a book, but also get hands on experience with the language. That's where I found Clojure a good choice for me since I could work on problems of interest to my work and reuse existing Java libraries.

Joy of Clojure also presents a persuasive argument in the opening chapter for Clojure, Lisp and functional programming. There is a pdf of that chapter available for free from the author's website:

http://joyofclojure.com/