I get where you're coming from, but I don't necessarily agree.
Odyssy and the upstairs of JII are HUGE dead spaces that could be used to add a lot to the guest experience.
Obviously attractions like the Imagination ones and UoE also need to be more of a draw, but the parks need smaller things in them as well.
Yes, there are dead spaces I'm not disputing that but just because a building is open doesn't mean that it isn't a dead space either.
In recent years, Disney has underbuilt parks and expanded as needed (or slower depending on who you ask). This helps to eliminate these empty buildings and problem areas. This was the approach taken at MGM, DAK, Hong Kong, and Studios Paris (DCA wasn't underbuilt, it was just cheeply built).
Compare those underbuilt parks to Epcot which within a year of being built was very close to what it's capacity high point was, and by 1989 (Norway and Wonders of Life) was at a higher capacity than it was at now. During that time, nearly every attraction was a perpetual walk on. In it's day, this wasn't reflection of the attractions found within, but a reflection on the ridiculously large capacity for the park. To "solve" this "problem", meant outright closing buildings that were "unnecessary" to staff.
Epcot had a good lineup of dark rides, but those rides didn't have the same appeal as the lineup in the Magic Kingdom, even though capacity wise it exceeded the Magic Kingdom. That's how concepts like Project Gemini come about; and while it didn't come to fruition, Future World is 100% different now then 1995.
Like them or not, attractions like Test Track, Soarin' and Mission: SPACE drive attendance at that park along with Illuminations and World Showcase dining. The large capacity of that park is somewhat wasted. If an attraction can push through 2000 people per hour, but only 1000 want to ride it, then something is wrong.