Also, bear in mind (especially considering the kerfluffle going on in the Thomas Kinkade thread about what is art) that a significant portion of the value of this photo is historic. That quality supercedes any artistic merit or lack thereof of the image. It is much more likely than not that this will only increase in value over time, because it is a piece of history, not subject to changes in taste. The Gursky may well drop in value in the future if/when his work falls out of fashion.