I don't know much of C++, but I did program in C long ago. C++ kind of scared me off back then, because it wasn't widely used, and it seemed unnecessary to me. The scene has changed a bit, though.
In my opinion, any programming language, if you have a good reason to use it, is useful to learn. C++ can be used to create pretty much any software project, so it definitely should be considered useful. I'd also venture to say that once one learns C++, pretty much any other language should be easy to learn after that.
On the other hand, there are some definite drawbacks to using C or C++, if you don't need it's unique abilities. While some prefer such things, I have moved away from statically-typed, compiled languages where you have to manage every aspect of your program's memory usage yourself. I don't need that.
There are some solutions to make memory management easier, though. If you aren't careful about how you develop in C++, you can get some very hard to find bugs with bad pointers and such.
It does have a huge amount of libraries that can be used. All of them aim to make certain tasks easier. Just have to be able to find the right ones for you, which can take time.
Anyway, if you anticipate speed problems with your project, it's definitely a good solution to that problem.