My limit is what I like...so if I don't like it, I don't buy it
I have sold many firearms and then any money made went back to guns. So i have a collection. My wife was skeptical about the whole "guns are an investment" thing but I proved it to her. I don't buy brand new glocks and then say "I paid $400, now they're $600" I might buy a WWII P38 for $500 and sell for $700 - and actually net something. Then I reinvest the $700.
We do also have our accounts split. She was costing me too much gun money when our accounts were together
She does still nag sometimes. Sometimes she thinks it gets in the way of us moving (I buy guns with the money that she would put in savings). But I tell her that I make more than the bank pays. Then she says "but some you won't sell" and to that I say "but I can". We work it out and no matter what I buy, its usually peaceful now.