I've almost never had to write or read C in a professional capacity, but if I saw that the candidate was such a geek, it would certainly be a huge plus. There's a huge gap in professionalism and knowledge between people who choose software engineering as a trade because it pays well, and people who love it for the sake of it.

But there's a catch. Second kind of engineer is not only better, but also much more desirable and highly paid, so may be it's an indicator that you should check whether your salary range is high enough and your tasks are challenging enough for someone like that. For some (if not most) roles, 9-to-5, grunt work engineer that just closes tickets and doesn't write new languages in his spare time is really the best fit.