I would consider EMH a third major initiative to get people to stay onsite. In fact, we would not stay onsite without it (or if it went back to the old way of only 1 extra hour in the morning). 3 extra hours at the end of the day - especially if you go, as we do, in value season when the parks close earlier, and especially if you've got young kids and like to take a mid-day break - is very valuable.
DDP in its current incarnation is a nice perk of our already having decided to stay onsite - we can spend about as much as (maybe a little more than) we used to on food eating mainly CS, but we can try some of the, frankly, overpriced TS restaurants. If tips are removed and the current price stays the same or increases, well, then, we'll go back to eating mainly CS and going to a few special TS that we really can't find close to home, like Boma and maybe a couple others. I won't spend 20-25% more on food than we're used to spending to eat food that isn't that special, i.e., that I can get at home. And Chicago is no different than many other cities across the country in that regard. It used to be there were types of restaurants here that couldn't be found for hundreds of miles, but as Americans' appetite for ethnic/creative food has skyrocketed in the last several years, you can get World Showcase-level food in the suburbs, in medium sized cities, in college towns, etc. You can certainly get it elsewhere in Orlando besides WDW, too. And all for less than Disney charges.
Now, the one thing you can't get anywhere else besides WDW is character interaction with your food, but I'll confess that we don't do character meals. I'm sure those places will stay busy, but I would think that quite a few other TS restaurants will experience a sizable drop in attendance. At any rate, I can only speak for my family, and there are many TS restaurants that we would not go to if it weren't for the DDP and the inclusion of the tip in the price.