Marginal Revolution has a discussion about the way in which the relative wealth of cities compares to how wealthy they look. The general consensus seems to be that there are two major factors: the look of a city is something that develops over time so the historical wealth of an area has a great deal of effect (recent wealth or recent depressions take a while before they show up) and the difficulty of building (things that enable sprawl also tend to make cities look less wealth because the wealth ends up not concentrated).