I used hyperbole of course, but in fairness, I've spent on the order of several months getting into Lisp. Mabye it's because I didn't work with it exclusively (I've been told here on HN that you need to be immersed in it completely and continously) that I still didn't become OK in any semblance of the term.
But here's the thing: I switched to C# from VB.Net. Before that, it was VBScript (ASP pages) and even before that it was PHP and JavaScript. At no point did I stop in the language I'm currently working in to start learning another.
Until that changes, I don't see how it will help me.
Basically, I would say that what you are suffering from is a kind of mental block syndrome: you think in a procedural/imperative paradigm. All your listed languages operate in that paradigm. It's a very transferable paradigm, as it so happens. I can come up to (some approximation of) speed in an imperative language in under 2 weeks. In order to ship Lisp(Prolog, Haskell...), you have to break out of that paradigm. I am not condemning you, mind. It is what it is. Rewiring your head is hard, and often doesn't have direct results.
I can, however, ship with Common Lisp, because I've spent on the order of 5 years learning it and writing it most evenings. I am learning Clojure and am preparing to ship a (excruciatingly minor) product with that after only maybe two months of dabbling. This is possible because I've bent my head around into Lisp shapes.
It's also been said that some people have the shape of Lisp in their head, and when they learn Lisp, their heads fit it by nature, and other people don't have that innate meshing. I certainly found Lisp to mesh with my head well.
Oh yes. It can be hard to get started with Common Lisp, just in terms of getting an environment working. I have a tutorial site to help with that(plug plug plug): http://articulate-lisp.com/
That's why I never regretted trying to learn Common Lisp some time ago, even though I didn't ship anything into production, and why I really do enjoy doing the same thing with Erlang right now, i.e. trying to understand it and getting as comfortable with it as I can get (and preferably this time maybe putting something out there).
Both these experiences helped me see programming differently, a change of "paradigm" as you very well put it, so now even when I get back to Python or PHP I feel like I'm a better programmer. Plus, there's something to be said about the fact that always trying to learn new and interesting stuff and not only focusing on "shipping code" is what keeps one's passion at higher levels. After almost 10 years in this trade I've found that passion at what you're doing is a very valuable and in the same time very volatile resource.
I couldn't break that thinking in college and struggled every day of my software engineering course where we implemented a Pascal compiler in Scheme. It wasn't until 10 years later that I started to get a handle on functional programming, due in part to some trickle-down from my Emacs config files. :)
But here's the thing: I switched to C# from VB.Net. Before that, it was VBScript (ASP pages) and even before that it was PHP and JavaScript. At no point did I stop in the language I'm currently working in to start learning another.
Until that changes, I don't see how it will help me.