It's probably advisable to book if you will be going whether you get
free dining or not and you really want a certain resort/category, but keep in mind that you may have to change resorts or categories to get the free dining. Booking ahead won't get you any advantage on booking free dining since you have to call and apply it after it has been released for booking.
If you won't go unless you get free dining, I suppose you could cancel or move the reservation once you learn it isn't offered for what or when you want. But if you won't go without it, you might as well wait until it is released unless you really want the 180+10.