"Change is good".
While there will always be those who miss original rides and attractions from Epcot Center (myself included) and can argue how they better fit into the overall original concept of Epcot, the very idea of the forward thinking Epcot Center set in motion that "Epcot" would be ever-changing. Not to mention the need to change as Epcot Center's original take on edutainment was beginning to falter with the tech-savy, instant gratifaction state of today's society.
Of the recent major changes to Epcot, all seem to fit into the original dedication plaque that sits outside the park's entrance. Particularly this part: "Here, human achievements are celebrated through imagination, the wonders of enterprise, and concepts of a future that promises new and exciting benefits for all."
Test Track celebrates the wonders of enterprise, Mission:Space provides the concept of a future that promises the exiciting proposition that space travel could one day be available to all humans and Soarin' provides an imaginative bird's eye view of the land humans continue to shape.
I would still easily argue that Epcot of now continues the promise to "entertain, inform and inspire" as the original dedication plaque states. So the approach has changed from one where we practically rode through 3-dimensional history/text books to one that is a bit more edgy. Epcot of today is still as unique as it was on opening day and it remains the one major theme park that continues to find new and exciting ways to educate while entertaining and not boring its guests.
Happy Birthday Epcot...may you continue to grow and mature with the latest technology and achievements of mankind.