Most studies focus either on the store of value function of currencies and their role in foreign exchange reserves [see Chinn and Frankel, 2008, for a recent review] or on the unit of account and means of payment functions, including the invoicing of international trade [see Kannan, 2007].
It’s unclear how much of this improvement was due to the program, but I think there is evidence that it played a role, lowering long-term interest rates and raising equity prices and home prices, effects that have supported household and business spending.