Experimentation is a wonderful thing -- as long as it is coupled with private risk-taking. Here is The Economist's report of the state of the Disneys' new urbanist Celebration, Florida. A little too utopian to meet its promises. Read the whole thing.
Here is Wendell Cox's report of urbanization in the U.S. It is mostly suburban and exurban. Within that large swath there is, to be sure, experimentation and variety. None of it is "unplanned." The questions are always: (1) who does the planning?; and (2) is the top-down part light-touch enough to allow bottom-up responses to what consumers want?
Developers (private planners) want to succeed. To do so, they must fathom and decode consumers' wants -- and supply and price the package in ways that attract buyers and satisfy investors. Not simple. Are the people who can do actually this "visionaries"? By definition, yes. But not utopians.
"If you want to make God laugh, tell him about your plans." This is mentioned by a character in Amores Perros. It has also been credited to Woody Allen.