Disney can almost certainly raise prices even more and let service and maintenance deteriorate farther and still see attendance climb. This is because of the fundamental appeal of the parks (a product of the Disney and Eisner regimes), Iger's skillful management of the film division, and, most of all, Disney's completely unique place in both American and world culture. In that sense, yes, WDW may be technically undervalued.
But...
Even those who hate naysaying and dire predictions can admit that there is a scenario, however distant and unlikely, where all that accumulated good will can't convince a single person that WDW is a reasonable value. Say, a theoretical future, when one-day tickets cost $500 and guests routinely fall out of the open doors of monorails. And somewhere between today and that fictional park future is a breaking point, a spot at which enough guests will choose not to go to WDW that revenue begins to decline.
And once Disney hits that point, there's no easy way back. The good will collected over nearly a century, the product of a combination of artistic and business genius and an un-reproducible confluence of historic and cultural developments, will be gone. Lowering prices, frantically building, nothing will ever put WDW back in the unique cultural position it once enjoyed.
Iger can keep slashing spending and raising prices and revenue will continue to go up - in the short term. And maybe that's his only job. But at some point, it will irreparably hurt the future of the company. Does Iger have any responsibility for the fate of the company after 2021, or whenever he retires? That's the question that needs to be asked.