I noticed on the Disney Parks Blog, that they're touting the 1st Anniversary of the New Fantasyland, the largest expansion in MK history. To me, that may just be a technicality (as far as actual land development), because when the Tomorrowland expansion opened in late '74-early '75, that expansion included Space Mountain, Carousel of Progress, The Starjets, and finally (opening in mid-'75), the WEDway PeopleMover. Compared to the new offerings in the New FL, I'd give the largest expansion title to TL '75.