I think the limited time magic shouldn't just be week long, but a month long. The lineup would something unique at each park for the entire month for it to actually be enjoyed.
I don't have any detailed ideas, but some I thought of would be.
-October at Disney's Hollywood Studios at night Sunset Blvd transforms into Halloween 1939 with tons of themed characters and lots of lighting and project effects to simulate a storm coming with it all coming down to a simulated lightning strike at Tower of Terror.
-December at Epcot World Showplace transforms into a true Winter Wonderland complete with real falling snow, a real indoor ice rink, and a snow playground for kids with special holiday meet and greets.
-September at Epcot is Retrospective Days where specific showings in the Magic Eye (Imagination) theater reshow all the previous films shown at Epcot ranging from Magic Journeys to the Making of Me, etc. Old Epcot characters would make appearances and even a return of Surprise in the Skys might return.
-April at Disney's Animal Kingdom is an Earthly Celebration which would feature Earth Day exhibits, special character returns, food booths offering truly exotic food samples, and a party atmosphere throughout the streets.
-August at Magic Kingdom Tomorrowland comes alive for the Intergalatic Space Exposition which would brings a special show to the Tomorrowland Stage, lots of unique alien characters wondering around, and fun future that never was exhibits and activities.
-March at Disney's Hollywood Studios is Movie Mania with sets from famous films set up with Disney characters playing the role of famous stars. At night in addition to Fantasmic, guests can also view full showings of classic Disney films under the stars on a giant screen set up at the Lights Motors Action theater. On select days, famous movie stars will visit the Studios to limited engagement meet and greets. The Premire Theater will host question and answer sessions for guests wanting to learn more about the film business and special merchandise including an all access pass to the legendary "Disney Vault" of Disney movies will allow guests to purchase any Disney movie ever made.