I'm not really sure what "Does horizons fall into the category of absence makes the heart grow fonder?" means, but Horizons was the most impressive attraction Disney had when it opened. The technology was so state-of-the-art back in the mid 80's that it was hard to comprehend how the things you were looking at were being accomplished, and this in turn made all "future living" scenes being presented seem like they would be plausible in the near future, or in the 21st Century. Epoct's slogan back when it opened was something like "the 21st Century begins October 1982" and the basic idea was that Epcot was a kind of "highlights reel" of things that would exist in the real world in the next 15 to 20 years.
I think the one of problems Epcot had was being right about some of it's future predictions, like something as simple as a "touch screen" which they had all over the place, at the World Key kiosks, Commincore, and Image Works... The touch screens were this "oh my god! how'd they do that?" type of technology that you'd never scene before outside of Epcot, but it's now become something everybody carries around in their pocket and doesn't think twice about. The other problem Epoct had was how wrong they were at predicting things the public actually wanted. "Cities under the ocean" was a theme at both Horizons and The Living Seas, but I'm not sure too many people were all that excited to live under the sea, just because it was "plausible" didn't mean it was appealing. The "cities under the ocean" weren't as exciting as the "touch screens", and the touch screens around the park stopped being exciting as they became common place in the real world.
Horizons was amazing when it first opened, but as time rolled on it started to seem less like a "plausible future" and more like a dated "sci-fi fantasy". If GE had stayed on to sponsor it, and it got an update every 10 to 15 years, which was the original plan for the Future World pavilions, I think the concept for an Horizons would still make for a compelling attraction, but keeping it state-of-the-art was the hard part, and whether or not people liked the "updates" would be impossible to know, and that's probably part of the reason they gave up on it.