I really think it's the design of the whole "Magic Your Way" packages. Disney makes it so the longer you stay the less you pay for tickets. So you only pay a few dollars more for a 7 day ticket vs. a 5 day ticket. Then, you can add the dining plan and do all the character meals your kids want...no paying $30 per person OOP. Plus, you can get free Magical Express to and from the airport and use Disney transportation while you are there. No need to rent a car. No need to eat offsite with the dining plan. No need to spend more $$ on tickets to Sea World or Universal when it's only a few dollars to add days to your WDW tickets.
They have the perfect captive audience. It's brilliant really. Why would a family not do the whole package? EVERY family I know that goes to WDW uses either the basic or deluxe dining plan. That's a lot of families. I don't know anyone that went to WDW in the last few years that DIDN'T use it. Including our own...we do the deluxe dining plan.
As for the food quality, I have noticed a difference over the years. Portion size has really gone down. Appetizers in 2003 were big enough for a family of 4 or 5 to share...I have pictures somewhere to prove it! In 2005 with the dining plan, the size of appetizers really, really went down. I think it's because everyone on the plan got an appetizer, so they became more single-serve portions. Fine for people on the plan because they all got one. Not so good for famlies not on the plan. Same prices, but no longer big enough for the family to share.
In 2003 we did a package called the Dreammaker Gold package. It was similar to what is now the premium package. It included 3 TS meals (It didn't matter if they were signature or not) plus all activities like water craft rental, Cirque tickets, free child care, etc. We could dine at places that don't take todays dining plans like Rainforest, Portabello, etc. The tip was included as well.
I can tell you that when CM's found out we were on that plan, they were thrilled! Almost every restaurant we had dinner at offered us lobster tail add-ons with our entrees because our plan covered them. In fact, they insisted we take them. Of course we took them.
Only 2 years after this, I don't believe ANY of these restaurants even offered lobster tail add-ons, even if you were willing to pay cash for them.
Now is this because of the new Magic Your Way packages with it's new dining plan, or is it because WDW cut spending for it's restaurants? Or is it both of those things? I really don't know.