Python will be more useful if you decide to do
    something with the language other than ruby on rails

If by "ruby on rails" you mean "anything to do with web development, deployment and server config management," then you'd have a point. Of course, when the context is a discussion about web development, then whether you can easly write OpenGL apps is irrelevant. Good developers also don't just learn one language and try to use it for everything.

    with it as well (SPSS, SciPy, NumPy and various other
    things)

That has effectively nothing to do with which web framework to work with. The OP has already worked with Java, C# and Objective-C. Assuming he comes across a project that requires something like SciPy or NumPy and assuming he doesn't use something from one of the languages he already knows, I'm guessing that he, like most hackers, wouldn't have a problem learning Python or another language no matter what web framework or language he had been using recently for web development.