I have been married for 19 years, brewing for 18. She doesn't drink beer, but we have an arangement.
1. Safety Equipment needs no permission. This includes the elimination of glass carboys, lifting, burns, and damage to life, limb, and property.
I have not exercised the full extent of this arangement, however. As I can use this for conical fermenters someday....but it has worked on:
large Hot Liquor Tank
tools to cut open kegs
hoses, tri clamp and myriad of other valves and fittings (little stretch here)
2. Time savings are also good candidates but need a little permission. Time savings means less time brewing and more with family.
Examples: Kegs, keggerator, and associated equipment. Grain Mill (less time at homebrew store).
3. Anything that "saves money" needs a little more explanation. Grain Mill and buying 50lb bags of grains, gallon sizes of Star San, and someday yeast lab....
4. Anything that removes impacts to rest of house: Fermentation cabinet, separate beer fridge, cabinet and storage to put all of this crap into and get it out of places she frequents in our small house.
The goal is convincing her that there are positive outcomes to all of this. I have used the argument that I am home in the basement rather than out pursuing other hobbies or sitting my butt on the couch watching TV. I often do the laundry while working on such projects (which also helps).
Lastly, she gets bragging rights on the block. My neighbor is a Senior VP of some national company (very successful)....but he is always traveling on business, can't make beer, and doesn't know how to tear apart a fridge and rebuild into a keggerator...skills and knowledge which I apply to other appliances and the home electrical and plumbing systems....nor does he have an awesome set of tools.
Really, my wife isn't dumb, she allows all of this because she loves me, and I am fooling no one.