Detroit? It's a cultural desert!
Chicago is a lot of fun, the Art Institute, Frank Lloyd Wright's Oakpark studio and surrounding area, John Hancock building (tip: don't buy the tour ticket to observatory, but go to the bar on I believe 87th floor, have a martini by the window and watch the panoramic view), Chicago Tribune building, Marshall Field's department store, world class Shedd Aquarium, The Magnificent Mile (your wife would definitely love it!), Botanic Garden, Lincoln Park (many chic restaurants and bars around).
For entertaining, Chicago has some of the best Jazz/Blue clubs. We spent a night at The Green Mill (4802 N Broadway tel 773/878-5552), there was in a seemingly rough neighborhood and there was a cover charge to enter the club, but the music was top notch.
Also when touring downtown core, take advantage of the free trolly cars or take the EL, get a city pass, just don't drive in downtown Chicago, parking is a nightmare.