I believe Jewell defines the onset around 1994.
...that's probably about right; I like to use Tower of Terror as the last example of Disney (well, at least WDW. We sometimes move well out of my realm of expertise when we start talking about the many and varied arms of today's Disney: The Conglomerate) going stones-to-the-wall, flat-out, giving it everything they had on an attraction. It's that kind of all-or-nothing creative philosophy that I personally think of when I consider "Disney Magic."
I think sometimes some of us barely miss each other in passing, with our conversations. My ToT signpost is useful to me, personally, as marking the spot where things fell over the edge, but I can understand that some folks might think the edge was reached before or after that particular point in time. And, even personally, I don't that signpost is useful as a marker between everything that Disney did "correctly," and everything done "wrong." There're a few oldies that, in my opinion, weren't done that great under old regimes, and there's certainly been stuff after ToT that I can appreciate, on some level or other (this is the point in the post where I typically mention how much I enjoy the Maharajah's Jungle Trek and Pangani Forest Trail).
To me, the ToT signpost is indicative of the point where the see-saw, in an overall sense, finally tipped past parallel. It's not the point where the see-saw, previously all the way up on the Magic side, suddenly slammed all the way to the Cheap side. But overall, I think the company has made a much higher percentage of cheaper, less Magical decisions in the time since Tower or Terror was completed (I've become one of those folks who feels that Eisner simply doesn't have the mindset to manage creative people, whereas Wells _did_ understand that dynamic).
Jeff