If you have Nature2 with its silver ions, then yes raising the MPS level high enough so that it will last over a vacation should keep the spa in decent shape. Without the silver ions, though, MPS is not a disinfectant and doesn't kill pathogens quickly enough. Also, technically, the EPA approval only came with this combination because of the hot water temperatures. Even so, lowering the water temp for vacation should be OK because the kill times don't have to be as fast as the EPA requires -- you just want to prevent uncontrolled bacterial growth. You don't need 6-log (99.9999%) reductions of E. coli in 30 seconds while you are away!