Well, you have to remember that very few places uses lisp for that very reason (the benefits don't outweigh the training cost), and the few production bits of lisp code I have seen work like java (albeit less object-oriented) with macros.

Second, I only mentioned C because of its use in understanding computers. Memory management is definitely a skill that people should (but often don't) learn in college, at least to understand what's happening when your GC hits some GC-unfriendly code. So I agree that memory management (via C) is a niche skill, so the analogy outlined in the original post doesn't apply... but quite honestly, how many people on this site write C regularly enough that lack of knowledge of C is going to seriously impede them? The vast majority of jobs I see are for PHP, Python, Java, and C#, at which point the largest impediment is the time it takes to get the O'Reilly book.