This is a really great point, most of my friends still don't use half of the features exist currently. I have no idea how you'd go about messaging that to users.
Of course this is not unique to menu bars, they just happen to be one established way to squeeze a lot of functions into a tight places. For a touch interface, we may want different ways to do that; but I'd argue that it's still crucial to provide non-hidden, discoverable ways to access all functions of your app.