Besides, erlang definitely gives you new perspective in building large scale system; supervision tree (let it crash), the actor concept, message passing, preemptive vm, built-in distributed erlang nodes, the repl, hot code swapping - any much more
The power comes from the whole ecosystem. Concurrency is built from ground up on language & vm level.
Can't emphasize this enough. Programming in Erlang will enable you to build novel mental models, useful beyond Erlang/Elixir.
Moreover, Erlang is a small language, and once you get past the unusual syntax, pretty easy to learn.
I work on a large scale production system in Erlang on a day to day basis; feel free to email me if I can be helpful in any way.
That said, it's an interesting platform that is a lot of fun, and its concepts can be applied to a lot of different platforms. Its inherent "treat everything as a self-contained service" turns out to be a fairly useful way to structure applications.
If you are not there yet, take every opportunity to learn a new language, doesn't really matter which as long as you have a good breadth (e.g. don't do entirely functional languages).
I think this really depends on some of those 5 or 6 languages being similar to the new one. If I know C, C++, Python, Java, Perl and C#, I'm not going to walk right into Prolog or SML or Scheme. (Your second paragraph is related to this, I just wanted to call it out a little clearer.)