I take your point about DC; it is the Land of Oz because of the federales. Wealthiest major city, seven of the country's ten richest counties in the suburban fringe, and all that.
That said, however, I think there are more cities with workable core neighborhoods than many think. I lived in New York for several years before coming to DC; it is full of neighborhoods. I have spent time in Philadelphia; I DON'T much like Philly), but it has interesting/salvageable/workable neighborhoods all over. In general, I think such areas are rather common in most cities that experienced most of their growth before WWII and the utter dominance of the automobile. These are less common in the West, where most of the growth is more recent, but even in the West there are "old town" districts that provide a nugget with which to work.
In general, my preference is cities that provide the widest possible range of options. I understand that many people will prefer the suburbs under any circumstances, even at the cost of being married to their automobiles, but on the other hand, it is desirable that cities be places where one can, without undue hassle, live, work, shop, and play without a car if that is one's preference. That means safe, decent, affordable housing in close proximity to major job centers; reasonably good urban school options; and a reliable public transportation system. Sidewalks and bike lanes are good as well. All this takes some attention in the planning process, or we are apt to end up with scattered commuter destinations linked by arterial highways, and no other way to get around.
I'm not anti-car (I have a daughter who needs to get to soccer games anywhere in the metro area ....), but I do think we are overbalanced in favor of the car. Preserving extant city neighborhoods is a place to start. Once cities reach a certain size threshold, the commuter system begins to become onerous and more and more people want to simplify. It's not coincidental that so many far-flung suburban sprawl jurisdictions out in strip mall and cul-de-sac land are now trying to develop coherent town centers and small neighborhood shopping districts. We find ourselves reinventing the past. If we planned for this from the front end, and tried not to destroy such areas where they already exist, adjusting over time would be much easier and cheaper.
I am in general agreement with your optimistic outlook for preservation and/or mix of neighborhoods but fear that the weak (or unreliable) links in the chain, as always, are the people who live in those neighborhoods. As the old saying goes: if it’s free then it’s not worth anything. And too many living in any neighborhood, region or city comprise Mitt Romney’s infamous-but-accurate 47%. Not only do they lack incentive to maintain their own surroundings but they have been conditioned to leave concern for and involvement in the larger community to someone else, usually a bureaucrat.
Finally, I admit that wherever I roam I pick up a copy of the local alternative newsweekly. These rags are full of wet-behind-the-ears raging lefties who want entire cities pedestrianized and suburbanites ear-tagged, branded and taxed merely for existing. They are quick to praise any building, block, or neighborhood in their city that has been revitalized by private capital and a lack of taxes/zoning restrictions. Of course, their praise undermines their own devotion to pedantic central planning and usury.
Invariably, an affluent crowd and the bright lights of an entertainment district attract the wrong sort of hangers-on: petty criminals, panhandlers and gangbangers. At this point the city has two options: pervasive East German style policing that stems the flow of riff raff but also alienates the paying customers or a lack of adequate policing due to a fear of Obama Jrs crying racism. It’s a tricky balancing act that few cities get right. When, as in the case of Cincinnati/Over The Rhine, both the city and the thugs get it very wrong all the best-laid plans are ruined.