It's kind of funny, when I go to a Perl conference, many people know me from perlmonks. When I apply for a job, people know me from conferences or from my Perl 6 work.
I got my new job through personal connections (some of which were made at Perl workshops), and the other applications I submitted contained references to github and perlmonks, and none of the interviewers mentioned either of those.
My current line would be "If I were looking to improve my Perl marketability for the future, I'd write tools that Perl programmers use".
I'd love it to be true that perlmonks increase marketability, but my own, limited experience can't confirm it.