Miami is planning to transform Biscayne Boulevard in its downtown into a true promenade. The Downtown Development Authority hired consultants to envision the changes, and the results are above. Below is what Biscayne Boulevard looks like today, courtesy of Google Street Views. Yes, that's a parking lot in the median.
There's no reason more American cities can't do the same - it adds tremendous real estate value and will enhance the quality of life of everyone except those wanting to speed through quickly. I'm looking at you, Western and Midwestern cities with really wide downtown streets.