3D was a brief fad in the 1950's, with another brief fad in the 1980's.
We're already at the "it's 20 years later" stage and I could argue that what you say has actually happened to some degree; the current influx of 3D movies has already lasted longer than either fad, and the technology to make them is *much* better than it was back then.
Yes, and during each of those phases/fads, they tried some things, and found that when technology/expense didn't work, it fizzled out. This time around, the tech has progressed somewhat, and the quality is better, Better, but it could always be even better. But folks seem to be saying that one day it should no "no 3D" and then there should be only R&D for 3D without any returns for the next 5-10-20 years or so "until we are there", and then suddenly we should get "perfect 3D". I don't think it works that way. We will always go through iterations until we reach relative perfection. And those iterations may be spread apart by decades, or may be contiguous.