I don't know about UNI, but Drake was limited in how big the Knapp Center could be just based on how much real estate was available on campus. The Bulldogs averaged between 9000 & 10000 at Vets Auditorium when I was a student, and I believe the original plans for the on-campus venue were for it to be approx 8500-9000 in capacity. But, given the footprint available, 7000 was all they could squeeze in.
Would I like it to be bigger? Sure. I also wish there was more non-street parking available in the area. But, when that place is full (which isn't nearly often enough), it is absolutely rockin' in there. I had several Creighton fans come up to me after the DU-CU game last season to ask if the atmosphere was always that insane. I also give Drake credit for building something on campus, something that none of the other private schools in the MVC have done. If Drake ever gets to the point where they're routinely selling out Knapp, then I could see them moving games to Wells Fargo Arena, like CU did with the Qwest Center.
If you look at the A-10 and the CAA, 2 "mid-majors" that are similar to the MVC in talent level, you'll see a lot of gyms in the 4000-5000 range, and a few even smaller than that.