It often does make in terms of job opportunities and salaries.
I'm sure many C developers would like to join new cool unicorn startup, but chances are this unicorn startup needs only ruby/js/go developers.
I think there are three (arguably four, depending on how you categorize) major programming paradigms. If you are competent in one, then learning other languages in the same paradigm is pretty easy because it's really just a change in syntax.
Learning a different paradigm is a bit more difficult because it requires a change in how you conceptualize the problem.