Shoot yeah, they are much cheaper, but is it worth it? If you're staying at Disney property, you have to get to your car, get off property, and find a place to dine. The palces around the World are PACKED and you will often have to wait for a table. Then, you have to return, find a parking spot, and travel back the parks - it takes awhile just to get in and out of the parks.
If you are staying offsite, it might be easier to do, since you could dine out for breakfast on your way into the parks and save that time (get up early enough to), and maybe dine out on your way home... but I wouldn't leave the park just to dine out to save a few bucks. Def not worth it in time and effort.
On your off days, or downtown disney days, or water park days, then it's alot more feesible, or if your family does a full morning, leaves the park in the afternoon, then returns later - you could eat on your way in or out.
we eat offsite only when we're offsite already. part of the disney magic, to me, is the dining exps. There are excellent places to dine there, that truly are magical and planning the dining is the most fun for me! we eat cheap already by splitting meals, big sit down lunch, counter dinner, breakfast in the room, take our own snacsk and drinks. its really not too bad =)