The catalyst for re birth of a city, imo, is the schools. People with money have choices, all that is left in the city are people with no choice except to stay.
If you have good schools (middle class would never have left), the next nut to crack would be mortgage money, lenders who would lend in the area.
Newly built urban areas attract those without kids. For the younger couples with no kids, that's fine till they have kids then bada bing bada boom, they are out of there. They need good schools.
Empty nesters? Grandma and Granpa will follow the kids eventually. Urban planners are missing the point.
