Here's my thoughts; having only driven through Detroit a long time ago. I've seen many other cities and towns, some successful, some not.
Urban planning is good, especially planning that forces people to live in the city by making suburban development difficult, as long as you do it smart. Otherwise, sprawl inevitably happens because it's the path of least resistance to actually fixing urban neighborhoods. Ultimately, sprawl is not sustainable because we have to drive farther and farther, waste more gas, be more isolated, etc...
Detroit needs to be downsized and a lot of it needs demolition. Detroit is one of the biggest cities in the US by corporate area, and has the most abandoned buildings for a city its size. But we can't force Bubba X from his house because he's a citizen, and he has rights, even though it makes no sense for him to live there at great taxpayer expense.
The problem is our antiquated and weak eminent domain laws, plus local governments that spread power to too many people. NYC has fixed a lot of that, Mayor Bloomberg took power out of the myriad of school boards, and other boards. We're in 2013 big cities, not little towns in New England, most people haven't a clue who the heck is on this board or that; they might know their mayor, and they know the President. So give that mayor power, because he's the only one that Joe Schmo holds accountable.
In a place like Singapore, I doubt Detroit would be allowed to happen. The Prime Minister there would have demolished and downsized the city already...but here, it's all talk, little action from the government. Something like Detroit, a national embarassment, ought to be handled at Federal level and fixed. The fixes are staring us in the face, but nobody seems to be able to get it done.
You need to be business friendly and tough on crime. The two go hand in hand...but again, we have political correctness, racial tensions, and all this other stuff that keeps us from doing what we should.
Finally, we have a failure of keeping it real. We live in a Democracy, which in Detroit's case, means the blackest, poorest, and least educated population in the USA is voting for those city council members and mayor. The people might pick a decent leader here and there, but can we really expect anything to change given who the voting base is?