While an A330 is cheaper then a 777 to purchase (and more expensive then a 787), if AC needed givebacks to afford a Boeing fleet renewal, I imagine they'd need em for an Airbus fleet renewal, as well. Then, of course, you have to take into effect the operating efficiencies the 777 has over the A340 and the 787 has over the A330/767.
As for the 767, Boeing did create a new interior for the 767-400 which can be installed in the 767-300s.