I live in Des Moines.
I'd save myself the trip to Winterset, unless you want to see John Wayne's birthplace, the covered bridges or Francesca's house... when I went to Fons and Porter's store, there wasn't anything there you couldn't get from the magazine.
I like The Quilt Block (that's where I got started)--there used to be another quilt store in Valley Junction but it's gone out of business. Creekside is worth the trip, and probably the quilt store in Ankeny. Ames has a really good fabric store, and the one in Indianola is good too, although it's been years since I've been there.
And a new attraction is the Pappajohn Sculpture Garden (outside, downtown). The Art Center and Salisbury House are also worth visits. The governor's mansion, called Terrace Hill, is an 1870s mansion, very interesting to see.
And there's always the big new mall, out west, called Jordan Creek if you're into shopping. There's also a revived part of Des Moines called East Village, with lots of interesting little boutiques. One of my favorite places is called Gong Fu Tea with all sorts of teas from around the world.