As I mentioned above, C# has actually added lots of the 'dangerous' C++ features, like raw pointers, and low-level performance tuning features, like explicit data layouts. So if you "fully master" every possibly usage of C#, then those skills will all transfer over to C++.
And C++ has added a lot of RAII features like smart pointers being part of the stl library.
I think that the language is moving in a direction that makes it really easy for beginners who have low knowledge of things like memory management to come in and write proper applications. Though you still have to learn the proper usage of such features since it isn't handled under the hood, it seems that both languages are advancing towards a common middle ground. But I'm just playing devil's advocate.
In the end, a programming language is just a tool. Like a sword-master, it takes a lot of practice to be proficient with your tool. I still say, stick with what you're comfortable with.
I do have a question though. Why is C# a "productivity language"? I've searched a bit and read couple threads on stack overflow but haven't found huge advantages in using C# over let's say C++ & QT. I've been programming with C++ for a loooong time now. Why should I pick up C# to further my productivity?