So, should the Statue of Liberty be stricken from Planet of the Apes because it is of the past and present? How about the Washington landmarks of Logan's Run? 1940's inspired fashin from Blade Runner?
Let's face it, barring a nuclear holocaust or other global disaster, some things are eternal. And some things are fads. The problem with some approaches to Tomorrowland is that it tries to anticipate the passing fancies of the future. Certainly, trying to predict the fads of the future will result in requiring a brand new Tomorrowland every couple years. But just as certainly, under the adages of "everything old is new again" and "classics never die," Tomorrow will be built from the foundation of Yesterday and Today.
Clearly, the Montana Future was wrong. Why? Because it didn't understand the fundamental difference between city and suburb. 1939's Futurama showed us a central city with everything we need in a city, a suburb that was as close as possible to living a simple country life, and transit that would get us between the two in the least amount of time. People of the 60s falsely thoguht we got all that, and it wasn't all it was cracked up to be. But, like Disney's TL 98 Imagineers, developers forgot the distinction between city and suburb, and both were blighted... Montana Future is perhaps where we want to live, and this suburban idea would be expressed well as a new House of the Future, perhaps installed in place of the Observitron, as part of a new plan for Innoventions, or built in the Autopia Zone. But the bulk of Tomorrowland has to represent a cutting-edge futuristic city, complete with public art, and visions of urban renewal and revitalization.
Think of it this way... Odds are, the Hollywood sign will never be in danger again. People have recognized that it is worth saving, and have put their money where their mouth is. The LA Conservancy is saving everything from historic homes to movie palaces. Thus, Tomorrowland can't be afraid of containing elements of the past. It simply has to be presented in a context of something the future felt worthy of preservation.