The suites took out a lot of seating. That number is accurate. This is why there were games last year that pretty much full stands, some folks on the hills and attendance of ~43K.
60,000 would mean an upper level to the bowl. A lower bowl would be a little over 50,000. I think you build the lower bowl with the ability to add the upper.
It's almost impossible for ISU to average 60,000 fans/game with Iowa averaging 70,000. That's 130,000 Iowans at a college football game about 4 weekends a year. Out of 3,000,000, it seems tough. IMO if we built 60,000 we'd fill it up sometimes, but unless we got really really good, and Iowa got really bad, it would be hard to fill week in and week out.
Can you imagine if IA and ISU merged and created the Iowa Cyclones. We bring both our fanbase to a brand new 150,000 seat stadium in Williamsburg IA. We would be the envy of the entire nation.