If you made a list of "failed" Disney attractions, Mission:Space might have to be on the list. It wouldn't be at the top--Rocket Rods was just a bad idea, and the track record on night-time spectaculars has not been great recently. I loved Rivers of Light and Harmonious, but I seem to be in the minority on both.
M:S was about $100M (or $165M in today's dollars) and clearly overshot the mark for the typical WDW guest. They had to neuter half the ride entirely, and if I recall correctly, they also toned down what is now "Orange" from the original.
Of course, I loved it, but again--definitely in the minority.