I assume that you want to be a good hacker. A good hacker has a healthy mix of knowledge that will allow him to start work quickly on almost anything. Without a solid grounding in C, (and a perspective of JS and Python), there are a whole class of things that you won't be comfortable working with unless you have some lower level experience.
With your current knowledge, how easy would it be for you to start hacking on an IP stack? Not that you would ever need to, but with a good knowledge of C such a thing becomes natural to you. All of those RFCs begin to make much more sense.
Another big benefit to C is how simple it is. You begin to see how possible it would be to create a simple C compiler, and this is a good spot for this intuition. It has a simple syntax, is somewhat feature-poor, and is very close to the hardware.
Plus, you'd be able to hack on CPython if you want ;)
Practical aspects:
Your knowledge seems to say that you are headed for web development, which I applaud, because all things exciting are happening on the web.
Web development is changing. It used to be that web developers were laughed at, considered to be inferior to other programmers. It has been a few years since I've seen that opinion, and I think it has been thoroughly shown to be wrong.
Web development has become, essentially, a two part system where the pretty web front end sits as an interface to a super hardcore back end. Web companies now face scaling issues that are relatively new to web development. While you may never program in C, having a strong foundation on what the underlying issues are.
Either way you look at it, learn C is to get a better understanding of technology. It will certainly do that for you very well.