I would definitely recommend jumping into the current API's and more specifically OpenGL due to it's cross-platform nature.
I generally don't like it when people give this advice. Yes, OpenGL is cross-platform, but anyone who has any experience with cross-platform (or even cross-vendor!) OpenGL development knows how much of a pain it is to get consistent results across platforms and hardware. I'd choose DirectX over OpenGL any time just to avoid the extension and driver compatibility hell.
I actually ended up going with DIrectX, via SharpDX. I'm not concerned with actual development at this point in time, and this is more of a side project type of thing than an actual career decision.