You really have to do the math for your family.
If you are planning to do a lot of character meals or are drawn to the more expensive ts entrees, it might be a good deal for you. Menus and prices are on the website, so take some time to scroll through, come up with an estimate food cost, pad it a little for safety, and compare it to the cost of the plan. Then remember that you've got to pay tips on all the ts meals.
For my family, the plan never works out. We did it twice and regretted it both times.
First, it ends up costing us way more. We do character meals and date night meals. We buy snacks in the park. We don't pinch pennies. And when it's all said and done, we're always under our food budget. I think it's because we don't always need or want a full meal for each person. Most of the time, when we each have a full entree, we end up throwing some of it away. We don't want to be stuffed walking around the park. We're actually happier eating smaller portions/sharing meals and eating a little more often. Or grabbing extra snacks instead of a meal.
Swapping a qs meal for snacks can actually come out as a good value, though, I will say.
I will also say, I have an autistic son who is a very picky eater and we often have to bring his food. But even with his cost taken out for comparison purposes, the plan still doesn't work for us.
Second, and worst for us - It isn't as flexible as we want to be
We find ourselves looking at the most expensive dishes so we get the best dollar value, instead of the meals we'd actually prefer. Sometimes we'd rather order apps or order a la carte instead of the entrees, and there's not way to swap. Sometimes we might want to change plans and cancel or move around meals towards the middle or end of our trip, especially if park hours change or new FP come available. But downgrading from ts to qs is such a poor value, it stings!!
I would only do the dining plan again if we did a short, adult on visit or if it was
free dining. But we usually rent DVC points for 2 bedroom villas, and the discount we get on the room cost is much larger than the savings of free dining in a rack room. So it's just not for us.
My sister's family, on the other hand, LOVES the meal plan and she doesn't care that it probably costs her a little more. We often travel together and eat most ts meals together, but she really prefers being on the plan.
We put our vacation savings in a separate bank account so it still feels all inclusive to us. A few days ahead of time I'll get Disney cards at Target for the 5% savings, just enough to cover our known expenses. So that saves us a tiny bit, too. I don't do it in advance because I don't want my money wrapped up in a gift card that I can only spend at Disney.