It's quite simple. It's actually already been done in Phillie, New York, and the entire province of Ontario: Abolish as many of the local jurisdictions in the Detroit area as possible, including Detroit proper. The resulting super-municipality would look great in national city rankings. This would help the suburbs, they'd no longer be "a hi-rise bolted on to the ghetto" to paraphrase a quote frequently attributed to their dear leader. It would have a tax base, there would be one guy whose entire job was to ensure blacks and whites stopped arguing about stupid bullshit that happened in the 70s, and it would have much better numbers then every other rust belt city.
The basic structure would not be what they did in Ontario or Phillie, but NYC. Boroughs will be necessary because nobody wants to give up significant elements of autonomy, even if the autonomous unit in question is a glorified tax-dodge (I'm looking at you Grosse Pointe Shores). The new Boroughs would take on a lot of the functions of their local Board of Education. They'd also retain most of the powers of the local cities. The City-County of Detroit gets police departments, County Government functions, functions the cities have already sent to multi-government agencies. Transit, for example, is by and large a fief of SEMCOG.
The pros for the City proper would be twofold. First: with no shitty headlines about how Detroit is worst at everything it would be a lot easier to convince people to move to the City Proper. Second with access to the entire region's resources we might be able to get a handle on crime. Get a handle on crime and Auto and Homeowner's insurance rates fall, since Detroit Auto insurance alone typically costs an individual $1,000 more then if he lived in Dearborn, this makes it much easier to stay in the City. If those things happen property values go up, which means property tax receipts go up, which means the schools district can afford to stop sucking...
The advantage for the rest of the region would be less, but would still be important. First, it would mean suburbanites gained a measure of control over the Detroit-brand. They had no say in whether Kwame got fired, but they definitely suffered when he did his thing. Second it's really hard to convince people to move to suburban Detroit from outside of the region when your entire sales pitch is "this tiny little suburb you've never heard of is not a hell-hole, unlike that nasty City of Detroit." Third a lot of them actually want the things that can only be provided by a real Metro Government, like mass transit