BetterSense it is real basic. When questions like this come up my girlfriend says, "You have spent your working years up to now earning money to buy things that other people thought they needed or they wanted. Now you have earned the right to buy things for yourself without having to justify or explain. If you will be happier having it and will use it, then certainly you should go ahead and buy it." This covers cameras, lenses, darkroom equipment, photographic supplies as well as parts and build ups for my offroading 4x4. [The list is much longer.]
She also said that if your wife does not like hearing that, then my girlfriend would see if she can find "a line item replacement" for your wife.