If JB is the anti-christ, the devil at least has a sense of humor. I don't know what his urban policy du jour is, so I'm not defending him in this context.
> 'repopulate' the city center after years of downward economic spiral,
> but... isn't the city center already populated? The idea is to just move a
No. There are often tracts of vacant or underutilized land in cities. Be careful about the term "center." In urban discussions it may refer not to the central business district, which indeed is usually fully utilized, but to the city jurisdiction itself, since the context for analysis is the metropolitan region.
> different set of people in, and ignore the people who used to live in the
> building replaced by an upscale condo - perhaps pay them relocation costs
This is an important problem. We talk about making cities better places to live, but in a market system this should cause a relocation of population; those who can outbid others for the better places to live will do so. If necessary, they can bribe the less-well-off to leave. The best way to improve cities is to improve the personal income of those who reside there.