I don't know. It's hard to say. Although basketball may be the primary driver behind these arenas, the University views them as multi-purpose facilities, so the capacity needs vary.
Baylor couldn't fill their old arena, despite their success. Baylor is also a smaller school in Waco, Texas. Compare that to Austin, TX where they built a new 15,000 seat facility, but just using creative methods to close it off to 10,000 for Longhorn basketball games.
The Pete is still a really nice facility. Pitt's problem is the product on the floor, not necessarily the size of the arena. An arena doesn't necessarily have to be jam-packed to create a great environment.