Downtown needs a grocery store, and maybe a "staple" store or two. If they sucked up the non-church/non-female barbershop quartet remnants of Southridge mall (i.e. a Target-like store/ Trader Joe's, a Younkers and a Sears) I think that would be about perfect. Cover most of the bases without having to leave the downtown area.
While this would likely help Downtown as a retail area, this is in fundamental opposition with the thinking of pretty much any downtown/Main Street coalition in Iowa (and beyond). I've worked in the marketing office of malls, and have also worked with the Main Street board in a couple of towns - they don't WANT big stores and chains in there. They all are grasping tightly to that "small town Main Street" feeling (even in bigger cities), where all of the stores are locally-owned and support the local economy. While this is a noble cause, complaining that the big stores/malls get all of the business and blaming everyone else for the shortcomings inherent to this business model. Unfortunately, we as a society are lazy - people want to go to one shop (Target, the mall, etc.) or, more accurately these days, the internet for their goods and services rather than traipse around to ten different mom-and-pop stores. Complaining about it isn't going to do anything; changing the "downtown" business model is, and that's about all that will save them.