I have heard many times since I have been a member of this forum that some believe that the DDP has negatively affected food price/quality at WDW. It would be interesting, if the data exists, to see the average price of a TS meal each year before the DDP, and the average price of a TS meal each year since the DP was offered. Has the average meal price risen more quickly each year since the DDP was put in place? Everyone has their perception, but data doesn't lie. Food quality is so subjective that it would be hard to definitively determine that food quality has declined, unless a vast majority of visitors believe that is the case from experience.
I'd be surprised if the vast majority of people who ate at Disney in, say, the 90s wouldn't agree that the food quality is lower now -- or, at the very least, blander/more homogenized.
Who knows, though.