Okay, I don't want to confuse you even more, but the math isn't as simple as you might think. Disney charges $40/day (rounded) for the dining plan per adult, but you have to figure out how much you would actually spend, not what Disney charges. Let me explain...
My family of 4 eats breakfast in our room every morning, and we only eat at a table service 2-3 times per 11-13 day trip. When we average it out, including tips and TS meals, we average spending about $75/day on food and snacks for our family. (I have 2 boys, 9 and 11). So the value of the dining plan is not worth $160/day to us. At best, it is worth $75/day, but when you factor in $30/day in tips (you will be eating at a TS every day with the DP - so tipping every day), that drops the savings to only $45/day.
You need to figure out how much you would spend without the
DDP to determine the value. Still, staying at POP, the 40% discount may come to even less than $45/day, so I would probably take the DDP - but remember that if you eat at really expensive places, your tips will get pretty expensive. 20% of a $300 meal is a $60 tip. You could blow all of your savings in tips...