You made a good point about Notre Dame. However, in the case of BC, Notre Dame's refusal to embrace BE fb and using the conference for bb, was one factor, among others, why BC left for the ACC. BC knew they would be leaving Syracuse, Rutgers, and UCONN behind and would be doing a lot of travel down south. All this considered, they viewed the merits of the ACC outweighing a crippled (for the moment) BE for fb. Notre Dame's supposedly contribution to BE fb is promising another future game, making it three per year. In several aspects, BC's departure was more of blow to the BE than Miami and VPI leaving. It is a turf matter, and BC is deep into the northeast.
BE fb and the Big10 both need to forget Notre Dame if they plan any future expansion.
I agree with your sentiments re: BC. If BC was still in the BE, the conference could still lay a claim that it was the center for northeastern college football. Now, with Penn State in the Big Ten and BC in the ACC, that claim is severely weakened. Miami and VT joining the ACC didn't have the same geographic impact.
I've posted elsewhere that I think the BE needs a true radical transformation in order to retain its BCS bid. ND isn't joining a conference any time soon (I think they will eventually end up in the Big Ten because it makes too much sense for both parties, but that may be literally decades away or at least until ND can't get its own TV contract anymore) and no school like Penn State is going to leave the financial stability of the other 5 BCS conferences to join a BE conference in flux.