We did it this past trip and will do it again but we are people wholike to have a sit-down dinner every night on vacation.
We also did it because we had planned on doing several character meals, and when I found out about the dining plan and did the math we saved a lot of money.
I think it is only a good plan if you would have gone to the TS restaurants anyway, not if you are only going to them BECAUSE you have the dining plan. We would have gone anyway to those character meals (5 of them!), so the DDP was a G-d send to us!
We are also planners (I am anyway, DH is not picky about where we eat), and I was one of those people on the phone at 7AM exactly 180 days before check-in, confirmation number in hand, to make all of our ADRs! I did research for 2 months beforehand to figure out exactly which places we would eat dinner. Also wanted to keep to the dinner times of our kids, so making ADRs was not a problem...spontaneity for dinnertime is not an option for us with 2 little ones who get hungry when they are used to eating dinner!!