Here is an article from the Christian Science Monitor asking the question many Joplinites have been asking: Should "tornado tourism" be encouraged?
Having been there three times since the storm, I suggest the short-term answer is "yes" and the long-term answer is "no."
A friend of mine, who was just there, told me today that they are making great progress. But, as the article points out, the vacant lots at the moment far outnumber those where building is occurring. So, traffic is low on those streets and the "tourists" will spend money and help boost the battered economy.
So, for the short-term, a tornado tour, along with the other attractions such as the mines and Route 66 seems like a good idea to me.