With current benefits the people I know who stay on site stay because of the benefits including the dining plan. My understanding is when you compare the type of hotel you would stay at outside of the resort with the type you would stay in on site you can get some pretty good deals with the benefits included. Now if they start to take away those benefits people will start to recalculate those decisions.
My friends always stay on site and stays within walking distance of Epcot because that is their favorite park. I think they can walk to DHS too. So for them they only need a bus for AK and MK which they are skipping AK this year. They are also huge fans of the dining plan. They did not do it the first year and my understanding is they regretted it and have saved money doing it every year after that. And this is coming from someone who is pretty cheap and honestly could care less what he eats. He also crunches numbers like you would not believe and is pretty anal when it comes to planning. So I trust him when he says the dining plan has saved them money and they really enjoy it a lot. Staying off site means they would not be within walking distance, nor would they be able to do the dining plan, nor would they be able to do FP+ 60 days in advance which is huge for them since they have kids who want to do certain things like Mine Train and M&Gs. They avoid EMH day parks, so that benefit going away would be no biggie to them. But if they start touching the other stuff, I could see them being turned off. But right now they love their Disney vacations and come yearly. They are on no forums, are nowhere near pixie dusters, just a general Pittsburgh family who loves a good family vacation.