The stadium is nearly full for every game.  I think the capacity is around 45k or so.

I looked at last year's stats and UCF averages 37k per game.  USF similar.  Memphis 36k, Houston 32k.

The biggest thing people look at is product on the field.  Boise has a ton of national respect, and a lot of fans watching because they produce on the field.  No one thinks less of Boise or Utah because they play in front of less fans than BYU.