I see what you mean.
Your description of the development in Atlanta, GA seems to be a good example of what I've understood to be the case in many big cities in the US.
Some differences between European cities and American ones is that
- In the US, you often find the least attractive areas rather close to downtown, even if there also is the phenomena of gentrified midtown areas like you mentioned, while in Europe, especially Northern Europe, the least attractive areas are rather newly built concrete suburbs far away from the city centre.
- "Downtown" in the case of US cities often refers to a corporate dominated area in the US, while the central part of most big European cities often consists of a combination of shopping areas, business/financing activity, expensive condos and cultural treasures like palaces, monuments, parks, museums, ancient structures etc.
- The most expensive single houses in the US are often large, newly built ones in the outskirts, while in Europe, the most fashionable way to reside is often living in a large old villa not too far from the city centre or even better, in a palace of your own IN the historical city center (but now were're talking things that very, very few Europeans can afford).
Anyhow, an interesting thing here is that while Harlem of today again has become an attractive area, I doubt a concrete suburb like Bergsjön in my home city, Gothenburg, will ever become attractive. Today, some people there are among the poorest in Sweden. Others who live there work for Volvo, SKF and other big employers here in Gothenburg and earn $70 000 a year. If the regional economy continues to develop in the right direction, the latter group will move out instead of using money "improve" their home.
A place dominated by immigrants called Angered here in Gothenburg is a bit of an exception. Many people originating from Chile, Finland, Iran, Iraq, former Yugoslavia etc, who've been successful here in Sweden have built really nice single houses close to the former ghetto like housing structures they once lived in. Partly, I think this is due to the fact that the nature in that area is really beautiful with forests, small lakes and so on, but apart from that, I think Angered, the place they once settled in after fleeing war and mad rulers like Khomeini, Saddam and Milosevic or unemployment (in Finland) has a special meaning to them. It gave them a new start and now they don't desire to "flee" a second time in life. Perhaps Bergsjön will develop like that too. Rosengård in Malmö however will not, there's no room to build single houses.
In the end, all healthy urban development depends on healthy companies and sane local government. Many large corporations around the world have managed to provide their employees with attractive housing. In my home city there were several such areas built in the 19th century and even later on (and they're still attractive).
I suspect that if a large Gothenburg employer like Volvo would've have been allowed to take care of these things in close cooperation with its employers in the 1960 - 1970 period, they would have achived something much better than the concrete suburbs government "social engineers" did. Probably small single houses that were mass produced, yes, but also very affordable and built in a manner that still would attract people of today.