One thing I've tried to make clear in my posts about urban and suburban hellholes is that I think that very marginal changes can lead to great improvements. The problem is that both, in their own way, suffer from being too-dense-but-not-dense enough. Or at least not dense in quite the right way. In many suburban areas what this means is horrible traffic jams, and in urban areas this means that absurd parking requirements and other bad policies reduce the good aspects of density. This is not to say that "increased density is always good," it's just that congested suburbs can, through better design, be fundamentally suburban and car oriented without being quite as car dependent, and urban areas which car-i-fied themselves too much can embrace the strengths of urban existence by understanding that the best path is not becoming a giant parking lot for hoped for suburban visitors.
In cities, improved mass transit is key. If you're in St. Louis, bring on the SUPERTRAINS!
