The bump, if any, would be short-lived. About a half-million people visited the Bill Clinton library in Little Rock, Arkansas, in the 12 months after it opened in November 2004. By 2008, the flow of traffic had been nearly halved.
As presidential libraries become more numerous, they may hold less appeal than they once did. The George W. Bush library in Dallas had some 60,000 fewer visitors in its first year than Clinton's did in its first year.
Attendance in all of 2013 at the George H.W. Bush site in College Station, Texas, was 130,000. Wrigley Field normally pulls in that many people in a four-game homestand.
"In Chicago, I would expect the largest single population of visitors to be local, so the net economic impact is close to zero," University of Chicago economist Allen Sanderson told me. Sure, every schoolkid in the metropolitan area might make a field trip there. If so, it would be a field trip diverted from some other local institution.
Texas ought to be the model for attracting presidential libraries, since it has more than any other state (one for each Bush and another for Lyndon B. Johnson). How much funding has the state government provided to those institutions? Not a penny.
It's always possible that Obama will choose some other city for his library. But his alternatives are not that great. Honolulu? No one would fly to Hawaii just to visit a presidential library. And once they arrived in that tropical paradise, most tourists would content themselves with other pleasures as they always have.
New York? Good luck finding an affordable building lot -- and good luck standing out amid everything Manhattan has to offer.
Chicago has more to offer the Obama library than the Obama library has to offer Chicago. So the state would be wise to save its money and take its chances. If the price of luring the 44th president is $100 million, let someone else pay it.