i think you hold somewhat of a romantic notion that probably would've ran into the brick wall of reality somewhere not too long after the 60's with the Disneys...
...remember they almost bankrupted the thing in the 80's...and the ridiculous (and still somewhat secretive) actual costs of EPCOT Center had alot to do with that. In most ways...that was the last time disney "footed the bill" for "doing it the right way or not at all". they had financial partners for what i would consider the 3 parks since EPCOT to open that were done the right way.
so really...from where i'm sitting...that idea died not too long into the future after disney.
the modern disney we see now...mostly in timeshares...is a different animal. All "development" is done from a cost accounting standpoint. It is never to innovate or entertain (at least...not to the point where that is a higher priority than revenue).
Now...we get some cool stuff...occasionally they bite the bullet - as with California Adventure - and open the purse to do things we can see the benefit of frontline. but these occasions are increasingly rare.
Look at it this way...Animal Kingdom and MGM offer nowhere near the overall guest opportunities that EPCOT and the Magic Kingdom do. No matter how much you may like those parks...the simple numbers can't beat this premise. Now, logically...Disney would have the re-investment and future expansion of those parks at or near the top of their capital investment and planning strategies.
But let's face it: they don't. I have no confidence that we will ever see the kind of investment and expansion that those two parks need to draw full day crowds. Never. some new toys...rehabs and new fads put into stores...but not real development as in the california adventure repair or even the magic kingdom fantasyland upgrade.
I have no doubts that this is intentional...they want people to funnel into EPCOT and MK at night because there are higher profits to be yielded from what they built and developed there 30 and 40 years ago. I have no illusions.
but i wouldn't think that somebody of the walt disney mindset would be ok with that....build it right or not at all. those two florida locations are not right - no matter how much you like the "detail" of animal kingdom (a popular excuse/ delusion of those that seem to want to defend the shortcutting of it)
But hey...what do i know?
remember also that the only "duplication" that Walt "allowed" Roy to do was the MK in Orlando....no others existed before they died. And i don't really know if you understand the dynamic quite right. all biographers seem to indicate that Walt was the little brother (though more charismatic) who kinda begged his older brother to get the money for his indulgences (the disneyland tv shows to fund Disney with ABC being a notable one)...i firmly believe that that was the case: Walt was an overgrown child with not nearly as much care for the money that he spent as he should have had...
much like my wife

...but being Disney fans - we all wouldn't have wanted it any other way.