This kind of description of urban development -- totally abstracted from demographic and economic changes -- is exactly what's wrong with your "thems" description of urban planning battles. One of the signal realities of New York since 1980 has been massive growth in population, with estimates of almost an additional one million people flooding into the city and another million or more expected by 2020. New housing stock has not kept up and the inevitable result is massive increases in housing costs, driving gentrification automatically.
On the middle income side, I'm part of the gentrification of Harlem as there is nowhere me and my wife could afford to live south of Harlem in Manhattan or even much of nearer Brooklyn. And we're already looking for where we will have to move as rents rise and we are driven further north or into the farther reaches of the boroughs when we need a bigger apartment for kids.
The real problem driving gentrification is not planning in the city but the lack of planning for the last few decades. Less than 8500 new units were built each year during the 1990s. So according to housing groups, the city added over 456,000 people, while constructing just 85,000 new housing units.
The real issue is housing and those who block new developments are a large part of what's driving gentrification in the City.
Nathan Newman