Boy I think I took that advise from the wrong source.
Math can make me a better programmer.
Statistics can make me a better programmer.
Accounting can make me a better programmer.
Biology can make me a better programmer.
Chemistry can make me a better programmer.
Building Macros and DSLs are the new Ivory Tower of software architecture.
I started out in 'scripting' languages, and I can even say that learning Java, in a group with some very skilled OO gurus, was a mind-expanding experience.
I have even seen it happen, en masse, at a company which was composed of various language partisans uniting under one roof. After exposure to each others' ways, I think we all become better programmers for it.
But on the other hand, the days where one could get away with treating 'LISP' as a proxy for 'Functional Programming' are long gone. Aside from the hoary old beasts from the 20th century such as Java, pretty much all the major languages have first-class procedures and suchlike nowadays. LISP is no longer distinguished by having good support for functional programming; it's distinguished by lacking good support for procedural programming.
Spend a few months to find a reasonable ecosystem (NB: the libraries, tools and community, not just the language), then move on.
But I did learn Haskell later, and I think that made me worse at the job (C++) I was doing at the time, because it gave me the habit of trying to write C++ in a functional style and made me more frustrated with C++'s type system.