I really love C# but it seems like a poor fit for doing what you really want to do ("get more involved in machine learning, data analytics, scientific computing"). It seems like a detour and not a step toward your goal.
At this point I am unsure if I should develop my C/C++ chops more or learn C# application development and add something new to the skillset.
I've used C# for computer vision, visualization and even for embedded stuff but it really isn't popular for "fun" things and I think it will be even less so in the future.