I don't think there's any doubt that Iowa has some great upland hunting. Obviously it used to be a lot better but loss of habitat and modern agriculture has had a big say in that. If they instituted mandatory buffer strips, their numbers would explode.
The selling point for nonresident hunters over maybe a SD is that you can hunt as many days as you want. Buy a license, and hunt the entire season. Whereas in SD you can only hunt for a total of 10 days. I think SD has better hunting, but Iowa is a good alternative if you don't want to hunt for days on end. There's a fair amount of MN hunters who live in the southern half of the state that can drive to Iowa for a day long hunt and then be back home the same day without having to worry about staying somewhere. I would personally rather hunt about once a week during the entire season than bunch all my hunting into one or two trips. That's just me though.
Just like anywhere else, habitat and weather are the two primary factors. Beyond that, hunting pressure will also limit your chances, especially if you are on public land later in the season.