How to Set Goals?

Although Simpson tells us that Writing Center mission statements should come from the university's larger mission (210), I'm left wondering how to set specific annual goals based on what are usually purposefully vague statements of purpose. She talks about using data to demonstrate how objectives are being met (211), but not about using data to determine what objectives should be pursued. It seems to me that you could come up with a pretty plan backed up by solid data, and still fall short if you can't defend the objectives themselves to suit the administration.