I don't think anything will ever balance attendance. The majority of people will always want Magic Kingdom no matter what as part of their vacation, and I don't really think rollercoasters specifically do much to solve that. Flight of Passage is probably the most significant crowd-mover in recent memory and is Soarin' with a cool ride vehicle.
This is the corner they backed themselves into by under-investing in WDW for the first 15 years of Iger's tenure. Magic Kingdom is perennially well attended, but the consesnus is growing that the park is lacking the sizzle that can be found in other parks. The classics are classics, but they should never be allowed to appear creaky, and they have been. The lead up to the 50th would have been the perfect opportunity to go through and make everything sparkle like never before, which could have staved off that growing perception and reminded us all
why the Kingdom is King, but sadly we all know how that went.
EPCOT, Hollywood Studios, and Animal Kingdom have long suffered from Little Brother Syndrome, but have not made the genuine effort to overcome that with investment and projects of sufficient scale. Hollywood Studios came closest to finally leveling up, but they undercut themselves by closing too much in the process. The effort has finally been being made to try to give these parks some
better attracitons, but for 20+ years they've needed both more AND better. So it's still too little, and still too late. While the last five years have finally given these parks a headlining attraction that command attention, they've all needed more than one of those, as well as a smattering of smaller attractions to help round out the day before and after you hit the new headliner. These parks currently have nothing announced that will move any of the needles necessary to pull genuine ground from the MK.
The result is that people come to MK, feel like it's a little dusty, then visit the non-MK parks and feel like they underwhelm outside of one attraction at each they felt took them to a brave new world. Which makes the rest of the parks
and the MK look a little dustier, despite costing more than ever and needing a herculean amount of planning. Which makes people start to look and consider other options for themed entertainment, some of which offer a bigger handful of shiny new attractions that take less effort to access, with more on the way.
Because Disney has gotten themselves to the point where any meaningful investment takes about 5 years from clearing ground to opening day, they've really got to take this summer to figure out that they've got to find some follow-through for EPCOT, DHS, and DAK if they want keep their public perception as top dog. Pandora, Galaxy's Edge, and Cosmic Rewind (personal feelings aside) are good opening acts for a genuine rebirth of each of these parks, but they need to keep that energy and double down. Give Animal Kingdom a new land with a big E-Ticket, 2 real, solid C-Tickets that don't throw you around, and nice Walkthrough and Sit-down Restaurant, (as well as a new Nighttime show - for real this time), give DHS a new land with a big E-Ticket, a D-Ticket, a C-Ticket and a solid Quickservice, and another new D-Ticket elsewhere in the park, and give EPCOT a new Pavilion in the front of the park with a substantial attraction (Imagination is the obvious choice) and a new World Showcase Pavilion with the same. Hold the restaurant, please, EPCOT has plenty at the moment. Pepper in some B-Tickets across these parks, to taste. Close nothing permanently to make these additions happen.
Magic Kingdom has TRON coming online and Splash Mountain heading down for transformation sometime in the short term - while Splash is down they should get something new into the old Stitch building to give Tomorrowland something smaller to see while guests are in Tomorrowland for TRON, cycle through some big plussing refurbs for the classics (Big Thunder, Pirates, Mansion, Peter Pan, Small World, Space Mountain, and even Carousel of Progress all deserve some infusion to look their Sunday Best).
I have absolutely no expectation they'll do any of this. But the problems they have and are on track to encounter can all be solved with money, and regardless of how they feel about spending they do have it. With the recession looming I'm sure they'll want to curb their spending rather than continue it. But this decade has the potential to be transformative for their business in the parks, and right now I don't anticipate it going the way they would want. Not without them bucking up and showing people who's boss.