The problems w EPCOT originated not from Walt's successors... but from Walt himself. Much like building the tallest building in the world and naming it "The Tallest Building in the World" is fine as long as it is still the tallest building, the idea doesn't work because every couple years a new building is taller than the last. So you can't really start a theme park and call it an experimental prototype, cuz that is only experimental for a couple years and then soon enough, it's old technology. Even things like Soarin (flight) and Spaceship Earth (spaceflight) are rather mundane. 20 years ago airline flights were a fun family adventure and spaceflight was inspirational and futuristic. Today taking a flight is a dreaded security line and battle over checked bags and spaceflight isn't much more than a canned government project. The tall building Walt envisioned... cool at the time, but if built back then, today would be dated. The monorail which was a neat alternative idea to automobiles, today is a maintenance nightmare and is cost prohibitive to expand.
This is a problem for theme parks which have to make a profit. When you invest in a new ride or feature for millions of dollars, you expect that feature to return profits in the form of drawing guests and getting them to pay money for the next 20 years. But a technology-themed feature is only going to be cutting edge for a couple years.
All that said, EPCOT is certainly not hurting. It can never be truly experimental, cuz it's just not realistic (or interesting) to showcase today's technology like building smaller microchips, LED lighting, or other real world inventions that are improving our standard of living, reducing energy consumption and so on.
This same challenge is faced by science museums all over the country. Their exhibits were neat when they were put in and someone got that bomber or submarine inside a building. But once you see it, it's not really all that cool the next time. What they focus on instead are simple concepts like wind tunnels, water play, vortexes, etc. Science bits that are easy to demonstrate but which have existed for thousands of years... they are new and interesting for kids to study, but far from experimental prototype concepts. These things work because they remain valid for years and years.
On the showcase...
Having a truly authentic world showcase is a nice dream, but inevitably it's going to feel like a well-themed mall, cuz that's what it is. It's a park in America, designed to bring bits of other countries to one tourist destination. It's not going to feel like you're really in China.
EPCOT as it is has a ton of draw. It's the 2nd most visited of the parks in Disney World, and it's also the one we spend the most time at outside of the MK. We'll typically hit up EPCOT for 2 days, but HS and AK for only a day.
There are enough unique places to eat here that it's not really perceived as eating theme park grade food... we come back again and again because the selection really is diverse. Not authentic food, but so many levels above theme park food that you'd get anywhere else. You really do get a little glimpse into each country.
The rides are great... 3 headliners plus many light well themed rides.
The Energy Pavilion... needs to go. And the Imagination pavilion needs an overhaul. Dated slow computers that you build a character on are hardly captivating to my 6-year old who has mastered Skylanders. They really need some quality development... integrate technologies and imagination / creation concepts like on the Infinity game system. But these things take time and money, then they only last for a year or two... so ultimately the goal of having an experimental prototype city of tomorrow is just not realistic. Keeping EPCOT a fun and interesting THEME PARK tho, is being done -- successfully, profitably, and most important -- enjoyably.
So what do we take away from this? Well, the only real problem I see with it is in the choice of name. It's just not an experimental prototype anything. A name more in line with its core values of science, nature, technology, and the world would have been more fitting. But if the only problem of a park is in the name -- well can we really say Universal Studios are "universal" or the Magic Kingdom is "magic"? These all incorporate misnomers designed to inspire rather than be accurate.
We always have a good time and keep going back. That is what counts.