Didn't you know, newer is ALWAYS better.
It usually depends on draw and upkeep. In Vegas, the old hotels weren't as nice and didn't have the same visual draw. I can't remember Horizons for some reason (probably because I only went once to EPCOT prior to 2002). I miss the Wonders of Life pavilion about our body with the great simulator (at least, I liked the ride). However, either Horizons was an upkeep nightmare, was losing popularity, or management felt that Mission: Space was a better draw. It appears that they might have been wrong.
Aside from that, I got nothing for you.