Here's a shot in the dark. With suspected favorite Michigan accepting an invitation to the Gator Bowl, the Insight Bowl is left with a choice between the Iowa Hawkeyes and the Penn State Nittany Lions. Both fanbases are excellent travelers, but since Iowa is much closer geographically, I believe that they will be given the nod from the selection committee.
As for the Nebraska Cornhuskers going to the Insight Bowl, it is my understanding that the choice is between Nebraska and the Missouri Tigers. When comparing the two squads, the dreaded "fanbase" argument also applies, and the Cornhuskers will likely show up in greater numbers than Missouri fans would.
Keep in mind that Missouri has a road game against the Arizona St. Sun Devils next September, and it's doubtful that Tigers fans will travel to Phoenix twice in one calendar year to watch a football game (though anything is possible).