I use to live in the suburbs around Chicago so I have a decent idea about whats good. Then again I lived there from ages 8-12 so my knowledge of the night life is limited.
Anyway Museum of Science and Industry was always fun for me, as it was a great mix of a traditional museum as well as innovative exhibits.
Welcome to The Museum of Science and Industry
Also if you're going to Chicago with the wife you have to check out Navy Pier, as it's one of the more frequent tourist spots (not to be confused with a tourist trap as many of the natives also frequent Navy Pier). You'll certainly find something to do down there.
Navy Pier
Sears (Willis) Tower and John Hancock building are a given. If you're going to Chicago you owe it to yourself to visit at least one of the two. I know the John Hancock building has restaurants and bars that can give you a view of the skyline at night so you certainly owe it to yourself to look into it.
Willis Tower - a global icon, a premier business location, a breathtaking skydeck view
John Hancock Observatory - Chicago's Greatest High
I also understand that couples enjoy visiting the Lake Michigan beaches. I know this because when I fell face first on roller blades into the concrete as a kid the first people to come to my aid were a couple.
Grant Park would probably be the Chicago equivalent of Central Park in New York and it will certainly look nice during a spring vacation. If nothing else you'll get to see where Obama gave his victory speech as well as where the Bulls held rallys after championship seasons. Speaking of which in the spring you could also catch a Bulls or Blackhawks game at the United Center.
I'll also second the recommendation for the Shedd Aquarium.
The Chicago Canal is also pretty fun as you get a nice tour of the sites as well as seeing first hand how a canal works (trust me it's more interesting then it sounds). If you go for St. Patricks day they'll dye the river green.
Still I can't help but strongly recommending late spring over early spring. Back in the days we would get snow storms as late in the year as March. May would probably be the best time to go as it won't be cold but at the same time you'll avoid the summer heat wave.