I was just talking with an insulator two days ago about the spray in method and he was telling me that they now spray the foam into the whole bay between roof rafters in a vaulted/cathederal ceiling , not leaving an air space for air flow from the eaves to the ridge vent, he said as long as it is filled solid there is no way for condensation to build up between the bottom of the plywood roof sheathing and the top of your old style insulation, so that being said I guess it could become feasible to spray the foam in between all of your rafters in the attic space as well as insulate your ceiling joist and as long as you have gable vents I bet your attic would be cooler by 50% or better and it would certainly reduce any transfer of heat into the actual living space, just a thought, sawz.