Paul Krugman writes about how the much greater degree of job sprawl in the Detroit area compared to the Pittsburgh area contributed to the substantial more severe decline of Detroit's central city, and therefore hurt the region as a whole. Stepping back, though, I suspect you'll find that this job diffusion is largely a consequence of the fact that Pittsburgh is home to two major universities—Carnegie Mellon and the University of Pittsburgh—while Detroit has only Wayne State University, a substantially less prestigious and influential institution. Detroit is fairly close to Ann Arbor, Mich., a great little town that hosts the University of Michigan, but that's very much a distinct place.
If you imagine an alternate reality in which the University of Michigan and the neighborhoods around it are tucked somewhere into Detroit and adding their mass to the hospitals and minirevival area downtown then you'd have a much greater agglomeration in the core of Detroit.
The overall higher education sector in the United States takes a lot of criticism these days, but in part precisely because of the things that make it seem kind of bloated and inefficient it's a very valuable urban amenity. Universities both create little neighborhood-level retail clusters around them, and along with medical facilities become the twin pillars of a regional knowledge-based economy. Of course cities can thrive without necessarily playing host to a prestigious private university or a public university flagship campus (San Antonio, for example) but for lots of older cities hit hard by the macroeconomic trends of the 1970s and 1980s the existence of major universities has provided a foundation for rebuilding.
Look at the difference between New Haven, Conn., which for all its problems seems to be basically on the urban renaissance bandwagon, and Trenton, N.J., which really isn't. The fact that Princeton University is 10-15 miles away while Yale is just a quick walk from downtown New Haven seems to me to make all the difference.