Hi Candice!
Although I've visited the Polynesian a number of times, I've never actually stayed. But my family and I will finally be staying there later this year, so looking forward to it "Big Time." :-)
In terms of the Concierge Service and/or the Disney Dining Plan, I think it will primarily depend on how you plan to spend your time at Disney: Whether you will spend a lot of time at the Parks or your resort, will most of your days be away from the resort (i.e. only there early morning or late evening)? Are you interested in character meals? Are hot meals a preference?
Besides having the convenience of this extra food around, if you don't plan to spend a lot of time at the resort, you may not get a good return on your investment getting the concierge service. As an alternative, I would at least look at the Disney Quick Service dining plan. This would feed you regardless of whether at park or resort, and you wouldn't find yourself keeping an arm's length to the resort just to be fed. The Concierge breakfast is continental, lunch is fruit and snacks, and evening is hors d'oeuvres. Again, good to have if your children are fairly light eaters, but may not work so much if they prefer a full plate with sides or larger meal portions.
So look at the
Quick Service Dining Plan, and see if that is a good match to your family eating habits.
And Good Luck!