Lots of intangibles...
1) Forces us to go to Disney, which we desperately want to do anyway
2) Sense of commitment. I am committed to Disney, in a way many other people aren't.
3) More casual trips. I hear people trying to enjoy their visit with maybe 1-2 days there, and I can't even fathom.
4) Part of why I enjoy Disney is the planning...I love planning. I don't mind "needing" to book at 11 months...that just means I lock in my vacation early, and I get ALL that time to anticipate it. My coworkers love teasing me about how early we schedule trips, and I get to use DVC as my excuse.