As for the other buildings, the ND campus is only so big and other than Saturdays in the Fall the Stadium and parking lot area are huge dead spaces. After Grace Hall, etc. they wanted to stop building "sky scraper" style buildings to utilize space on campus and looking at Grace Hall it's easy to understand why.
Having music classes in one of the buildings will be great for the marching band (which is at least tangentially connected to the atheltic dept.) and it's also much closer to the state of the arts performing arts center on the southside of campus for everyone else.
All of the spaces that they are adding will be used well and appreciated by the students. You could also look at it this way: the modernization of the football stadium (the necessity of which is often debated itself) wouldn't have been possible without piggybacking off of improvements to academic and student life buildings; and given that ND is a top 15 university it's not difficult to understand why improving academic facilities is important.
My own opinion is that integrating student life "into" the stadium won't have much of an impact one way or the other. It is a creative utilization of space, and students are already pretty into football. Will it improve the learning experiences of students who get to utilize state-of-the-art classrooms? Yes. Will it improve the gameday experience? Who knows (though I am a fan of jumbotrons everywhere I've seen them utilized well...sorry!). Will it lead to increased donations from alumni? Uhh doubtful.