Thy product on the field will determine e demand for additional seats. Iowa State is in unprecedented territory when it comes to season tickets and attendance. Another year like this year and 56k will be a fond memory. Investments in football need to be cautious and measured to ensure the investment is sustainable. 56k seats pulling in more dollars per seat is better than 60k and deep discounts or tarp advertising revenue.
Actually having 60k seats is better. Because for some games you will sell all 60k of those seats. In addition the extra 4,000 people buy programs, concessions, and parking. If you are going to do an expansion then you need to add some seats for revenue purposes. You simply can not just keep raising prices on existing seats. That is the surest way to empty the stadium as you will get to a point where you will price many people out. An extra 4,000 seats at $250 a season ticket is $1 million. And not having to raise the other ticket prices at all.