Building a fan base takes years and alot of effort and it only takes a few down years to lose it (look at how Illinois and Purdue have dropped off in attendance, yikes)
Scheduling opponents that casual fans want to see is one part of it and Frazier is obviously working his tail off on that with success to show for it, Kudos to him!
While the MWC would not be much of a financial move up, there are several more programs in that conference in both football and hoops that have had national success and publicity that would draw more casual northern Illinois fans to see the Huskies play.
Don't think that Utah and TCU have had an easy time building their fanbases and don't have competition for the entertainment dollar in their markets.
Hoops is hugely popular in Utah and the Jazz have been a top NBA draw for decades. Soccer is also very popular and the MLS franchise draws sellout crowds. Not to mention BYU which is the top drawing non AQ Division 1 football program(#28, 2013) and Utah State(23263, 2013) draws respectable numbers as well.
http://www.cbssports.com/collegefootball...wn-in-2014
Despite have a stellar season TCU's attendance is down from 2013. Utah's is up by 2%.
TCU being in the Dallas Metroplex has to compete with the Cowboys(America's Team and NFL's richest owner) Texas Rangers who have had MLB success, Dallas Mavs led by a charismatic owner (Cuban) and the Dallas Stars who have won a Stanely Cup in the last 10 years. Not to mention Baylor in nearby Waco and the pervasiveness of UT(#8) & A&M(#2)
As Frazier continues to schedule up, as long as NIU continues it's winning ways; Huskie attendance will grow.