"Cities (especially big cities) should no longer seek to extract the maximum amount of tax per piece of ground (resulting in only expensive developments) but should have policies that aim for maximum societal gain: this means building housing to the exact class percentages of the population. 10% rich, 40% middle class and 50% working class in the country? That's what cities should aim for."

This. Unfortunately it's fallen out of fashion... everyone wants to become the richest city in the world, even if all it means is that you will price yourself out of it, literally delivering it in the hands of the few 0.1% for whom it's just another new toy to play...