I hope Chicago doesn't get it. How boring. There is no great reason to host the Olympics if you're a city like Chicago. Economic upside? Maybe there is, but most cities lose money or break even. If they make money, it's not a lot of it. Yes, this takes "exposure of your city to the World" into account. Besides, why would a city like Chicago need more exposure?
And now that the security costs are so high, there's even less reason to host the games than there was 8 years ago. Even 8 years ago, the Olympics was arguably a bad deal for the host city, because it was hardly worth it. With security costs the way they are now, you're going to see more cities lose money rather than make money.
Now, for a city like Beijing, which is in a country that's going to become the next big superpower in this world, the loss of money is worth it (although I doubt they'll lose money on this). Why? Because generally, people don't know much about China other than really "Westernised" food that they eat in lousy restaurants. That, and Jackie Chan, and he's not even from China! What a great way to showcase your culture and city. When you hear the word "Beijing", there's a certain mystique to it because it's a big city in a big country that most people know nothing about. I can't say the same about Chicago, which gets exposure from so many sources. I don't think people are going to be so fascinated with Chicago after the Olympics that they're going to flock to the city to see it. Athens is different, as was Sydney. You know of them, but most of what people know about Greece are names of philosophers, names of Gods, tzatziki sauce, whatever. Sydney is in Australia, and is all about riding on the backs of kangaroos, right?
Beijing's tourism sector has a better chance of booming than Chicago's due to a lack of exposure other than in newspapers and economics magazines. People around the world have a general curiosity of China. Chicago is like New York City, Los Angeles, San Francisco, Paris, London, etc. I've seen enough photos, watched enough movies, and heard enough about those cities that even if I don't see them in my entire life, I'll still have an image of what it looks like and what goes on there (even if that perception is wrong). However, interest in Beijing or Mumbai would increase immensely, just like interest in Australia spiked and is still going strong.
PS: I have lived in London, Sydney, and have been to Beijing, Paris, etc. I'm not dissing those cities. I'm just saying that I believe Chicago wouldn't benefit greatly from hosting the Olympics as much as cities that get less exposure.