I find most mission statements, be they for a country club, museum, charity or whatever, to be BS. Most are generic, and who wants to be anything but the "best," "superior," or the "finest"? "Our mission is to provide a just-o.k. golf course and mediocre service to our members" would not work.
I actually like the statements in Bruce's posts on being: "one of the toughest tests" of golf and: "The mission of the founders of Hazeltine was to build and maintain a golf course suitable for the conduct of national championships." At least they are relatively specific and give a prospective member some idea of what he's getting into. I'd know not to put in my application.
Less specific is: “XYZ Club is a private golf club dedicated to providing its members, their families and guests with a classic, carefully restored and maintained golf course and superior golf-oriented programs, services and facilities while maintaining the legacy of our history and traditions."
However, all the general mission statement BS in the world does not help without some very specific guidelines about how the "mission" will be carried out. That is what really counts - the flesh on the bones. What those guidelines are called does not matter, whether they be "guidelines," a "strategic plan," an "operating plan," or whatever. What matters is having something concrete against which plans and actual performance can be reasonably judged or measured. What matters after that is having a Board that continuously measures and reviews its decisions and outcomes against those guidelines.