It would be a mistake to build a 45k stadium. Its a pessimistic viewpoint based on the past, not the future.
If you have a program stuck, and likely to continue, in a 30 year period of relative mediocrity, in a minor conference producing minor football revenues, with an administration that doesn't much care about the success of the football program and won't put money into hiring coaches, funding a recruiting budget, etc., then a 45k stadium sounds about right.
So the 45k stadium should have been built in 1985. It would've served Pitt well for these past three decades.
Is a 45k stadium what we need for the future? Well, given that all of the above factors have changed, I'd suggest, and hope that the answer is no. We don't need an 80k stadium for sure, but we don't need a small one either. Suppose our hope that the 412crew thing happens, and Pitt becomes a very successful program with continued success in the near future, based in large part on high end local talent. I can see us needing a bigger stadium for regular conference games, not just for ND, WVU, or PSU. Not huge, but certainly one in the high 50s.