Please correct me if I'm wrong but OSX has no high contrast - white on black themes. Also I couldn't find an easy/comfortable way of using the magnifier, I greatly prefer Win8's magnifier - it has a few limitations but I found OSX's one annoying.
From your descriptions of how you use of Windows accessibility features, it sounds like you've figured out highly efficient usage patterns and your facility with navigating the UI seems (to me) a bit higher than even many expert users. So, manipulating a different set of accessibility interface may not be comfortable or as useful for you, which totally makes sense. To answer your question about contrast:
OS X does have a separate slider and checkbox for contrast.
I don't use these regularly so can't comment on their usefulness. When I manipulate them, they do noticeably affect the display contrast, so much so that when the contrast slider is high enough, font edges of text and other UI elements start to wash out.
OS X does not implement themes and, like you, I would be ALL OVER a system-supported dark/professional theme. (With the latest version of OS X, Apple has introduced an extensions framework which opens a path to vendor-supported UI theming. But even if this is the direction OS X is headed, I would not expect custom themes for at least a couple more years.)
I have good corrected vision, so I don't use the magnifier regularly. I occasionally do fiddly UI work and it works OK enough for me in that instance. It has some customizability but not a whole lot.
On the customization front, I use a third-party piece of software that I sort of think of as my personal API for the UI (as well as much of the command line and UNIX layer). That software is Keyboard Maestro. It is definitely worth checking out if you regularly use a Mac-like machine ; ).