I would say to "right-size" Detroit, the new city boundaries should be from the river to Grand Blvd, and everything south of that forming the new boundaries. Basically returning to Detroit's 19th century expansion to the limits of Grand Blvd.

This would render everything north of Grand Blvd separate municipialities, including New Center, Virginia Park, Boston-Edison/Arden Park, Highland Park, Palmer Park/Woods. Traditional neighborhood boundaries west and east would also be recongized and allowed to secede from Detroit.

This is where a regional police, fire, park, transporation, and library systems would come into play. Wayne, Oakland & Macomb counties would share in these services, paid through taxation as a separate line item over and above municipal taxation which would take care of services like water/sewer, garbage collection, road repair, etc.

This would consolidate duplicitous services so each municipality would not have to establish it's own set of separate services. They could however opt to do so if they feel their level of taxation could support it- "The City of Palmer Woods" as an example could encompass everything between McNichols and 8 mile/Woodard to Greenfield, and may be able to support it's own city services without having to opt-in to sharing them with the region.

This would keep those communities who currently have their own services from having to give them up to a regional authority such as the Grosse Pointes, Clinton Twp, St. Clair Shores, Southfield, etc.

Similarly, municipalities could opt-in to some services, and opt out of others, as their tax bases will allow, making it organic in nature.

Certainly to begin with, the park systems, water/sewer, roads, libraries, transportation, could be regionalized as tri-county authorities.

Fire, police, schools could be locally run if taxes are sufficient to do so, if not, they could fall under regional authority as well.

Possibilites are endless, and food for thought.