we both have our own hobbies which have their own respective "cash outflow", and neither of us gets on the other about the related purchases. i dare say she probably spends more on her hobbies than i do--it's just that her purchases are $40 here and $60 there (and are pretty regular), whereas i tend to do a couple purchases per year at the $500-1000 mark.
the "trick" is that we've got a joint checking account where 2/3 of our paychecks go and we each maintain separate accounts which holds our "play money". as long as there are no problems paying the household bills, etc., i never get crap about what i might come home with or use my money on.
my wife grew up in a household full of music and players, so she understands. it also helps that our toddler is showing lots of enthusiasm and aptitude for it as well, so i can actually write off new (or used) instruments as "investments" and "hand me downs".
it also helps that i've been teaching her about the various aspects of music production, guitar sounds, etc., and she's starting to understand that you can't get the sound of a Les Paul out of a strat. she's learned to identify the sound of compression and autotune, so i feel like i've accomplished at least SOMETHING.
the only thing i've "snuck" into the house was a Tampa i bought from TKingen here 18 months ago. i bought it within a week of our son being born and money was a little tight, but i HAD to get it. it just "appeared" in the rack in the basement. she saw it a few months later and asked "is that new?" (hard to miss the glowing VU's), and i said "eh, i've had it for a little while", which wasn't a lie.
the only thing i've gotten crap about was my midiman keyboard/midi controller. she didn't understand why i needed a keyboard when she already had one that was "perfectly fine". and it IS perfectly fine.....except that it doesn't have midi capabilities and i can't control VSTs with it. i STILL get crap about that damn $60 keyboard.
actually, given the money i've put into the studio and assorted gear (and that which she's put into it via christmas, birthday and random gifts--she's bought me a Martin, a mandolin, an SP B1 and an epi valve jr), she gets REALLY mad when i refer to it as a "ghetto level studio".
as with everything else in marriage, communication and compromise is the key.
i remain convinced that Thomas Jefferson was talking about keeping the little lady happy when he talked about "Domestic Tranquility".
cheers,
wade