I guess I'm one of those wackos who doesn't think there's been a decline at all. There's been change, as some attractions close and others open. I wish Disney would make some of these changes quicker than they do. But no, I don't see a decline.
I do not see the massive decline either. I do see that DHS took a less then wonderful turn after they closed the studio and did very little to fix that, I guess relying on ToT and RnRC to take up the slack. Epcot did close a couple of attractions without replacing them, but, certainly not to the degree that DHS did. That place got really sad.
Part of the problem with DHS was reputation. Actually since it's opening it has been viewed as a half day park and didn't really acquire the need for more until recently. That, I feel, came about because MK was getting swamped and, to a much lesser degree, they were making Uni look better then Disney.
Epcot basically just changed most of the attractions in Futureworld, some for the better, some not so good, but, the area that they completely ignored since 1982 was World Showcase. The problem is that so many of the former Epcot lovers have never really been able to grasp the idea that things change. Everything that shows up is automatically considered a decline because it doesn't conform to the way they think it should be. However, that is mostly the sentiment of the people that tend to be attracted to this type of media that focuses on "all Disney, all the time".
Anyone with a supply of old pictures or a memory can easily see that in spite of Entitled Guests that have no concern over the property of others, it looks so much better then it did before. There are more flowers, brighter colors, more eye appeal then ever, but, again, so many focus on the removal of trees. That trimming back and removal has happened since the place opened, but, no one really noticed until recently. What that has done, in the positive sense, is opened the view up and not hide them like in a jungle. What is the purpose of building a beautiful fake castle and then hiding it from view?
So, to me, you are correct, there have been many changes, but, I have yet to see the decline and just a simple look at attendance backs that up. What I did see is a decade of little growth, but, that's known as stayed the same, not decline. It shouldn't have happened and now there are construction walls everywhere. The future looks like it might be interesting though. At 68 years old, I just hope I'm still around to witness the new Disney.