The difference between New Orleans and Detroit? It only took 2 days for New Orleans to be a ruined city.

This seems silly. Fix your economy and the gentrification of your urban area will happen all by itself. I would focus on:
1. Educational institutions.
2. Making sure there is good IP transfer from educational institutions to industry.
3. Making sure there is a VC community and the local legal framework is attractive to big business and small business.
4. Focusing on marketing the cultural aspects of the city so people will want to move there.

To hell with fixing up old buildings. People will buy them and do that. The government's job is to make the city a place you'd want to live. Cheap property is an advantage there once the reasons it is cheap go away (and my understanding is they've done a good job cleaning up some of the crime problems, so they are right where they want to be....)

RE: How NOT to rebuild Detroit