Sadly I think you are probably right. BU is so ambivalent about basketball that we moved our games back to the little high school sized gym upstairs. Even if BC were to ever come down and play at BU (not likely I know), I'm not sure we would even come close to filling Agganis.
Maybe having everything on one weekend is too much and makes for too busy of a sports weekend for everyone.
That being said, I would still like to see BU and BC playing regularly in basketball. It seems as if BC/Harvard have a nice series going.
Maybe if they somehow thought outside of the box with student tickets (even for the visiting teams students) etc, they could make this something of a "rivalry" game. Heck BU couldn't draw much worse than the UMass Lowell and Central Connecticut games.