BU, as far as I am aware, has never had an interest in those buildings and has worked with both the cities of Brookline and Boston to consolidate their real estate holdings rather than to expand them. There is plenty of opportunity for pre-existing redevelopment, including all those BU owned parking lots, that will be the priority before attempting to purchase up more privately owned land adjacent to campus.
The land grab (and small endowment) of Wheelock also gives BU opportunity for expansion with the newly established Fenway campus.
I have no idea what BU officially does and doesn't think about the tire stores on Comm Ave. Its my own personal preference that they should be gone.
Regarding Brookline, I also recall when the school of hospitality moved to their "new" building it was causing concern for Brookline because that property got taken off the tax roles, and IIRC the attached buildings as well were all willed or gifted to the university by the same owner. Not sure if the school ramped up PILOT contributions. They also seem to have taken over another office building near the West Campus CVS as well as converting the Landry's cycles into an expansion of WBUR.
There seems to be some movement of offices out of Kenmore square as those buildings have been sold over to that quasi-commercial stretch on the south side of Comm ave along West Campus. Not sure what will happen with the bookstore.