I say "yes" - languages are part of your professional tool box, and the more tools at your disposal, the better developer you can be. Noone is going to argue against the benefits of broader experience and education. You will need this to help you determine which tool is the best fit for a project. People who know only one language will want to apply it to every problem.

I claim that C is the language of choice for much of the open source projects that you will encounter over the next few years, for reasons of portability, speed and familiarity to a large number of developers (but mostly the first two).

If you find yourself building various tools/languages/kernels from source, then knowing C is going to be useful to you at some point. You will at least be more capable of diagnosing and correcting minor issues, providing better feedback to the authors, and ultimately providing patches yourself.