Gregory Maxwell wrote:
The problem is that participants would cheat by saving up photos. :) and even if they didn't we'd end up with lots of duplicate photographs of the same easy-subjects. :)
All the better! Then we can choose the best one for the article. The other ones can remain on Commons, but needn't be used in Wikipedia articles.
Also, I think such an effort would be a great idea. While it is true that there are currently many "easy targets", it's all the better, because then they will be filled with images quickly. The contest will gather more meaning later when all the "easy targets" are exhausted!