You're just not getting it.. SSE is a miserable comparison. SSE talks about the PAST. Horizons was dated because it tried to represent the FUTURE. SSE has been updated to upgrade it's show technology and add some freshness but the core presentation is roughly the same. Horizons could not have stayed the same with just AA and lighting upgrades like SSE had for 30 years. Your 'easy fix' of new music and updated scenes really means having to redo 3/4 of the ride. The IMAX films and everything beyond it would have to be rescripted and rebuilt to get rid of the old 80s style. The concepts of colonization, terraforming, and communications could still be there in principle, but not how they were represented from 1982. It works for SSE because burning Rome hasn't changed and won't change in the future. Our futurism has and will continue to change.
Even tho it was futuristic in the 60s.. you couldn't take the original Star Trek TV series version of the ship's bridge and pass it off as futuristic today.
Living with the Land is also a horrible example because the public's perception of agriculture has not advanced at the same pace as technology and style.
Horizons would have needed far more than show tech upgrades to extend it's usable life. The show as presented was doomed to a finite lifetime just as the final two acts of the Carousal of Progress are and Communicore was.