Tell your wife that there's absolutely nothing wrong with having more than one M64. If that doesn't work, gift one to her(maintaining it of course and occasionally checking it for function/accuracy)and keep the other for yourself.
The money you would spend on wearing out an M64 with +P ammo would be enough to purchase 75 more M64's. Don't even worry about it. +P is a marketing ploy,......it doesn't mean anything to a modern revolver. Might be a factor in an alloy frame five-shooter but not in an M64 which is a magnum except in cylinder length.