Harvard University, with an endowment of $32 billion the nation’s richest school, also heads the list of debtors, with $6 billion owed. The school recently unloaded the Arsenal office complex in Watertown for $168.5 million, which it purchased for $162.6 million in 2001. The school was on a buying binge, and clearly had no plans for the property. Lots of money, but no vision, no plan.