OK, serious/honest answer coming here.
Either she is legitimately concerned about gear purchases, or she isn't.
1) If you are having trouble making ends meet and there are unintended consequences due to your purchases that would indicate that you are truly gear-obsessed, then marry her. You need a referee and she knows you are nutty but is willing to try to help. That's saying a lot. So... Are you a Leo?

2) If she is just nagging about your finances, but is actually incorrect, then she has a jealousy problem, a control problem, or is perhaps a miscreant with a lack of proper social boundaries. So talk to her about it to remind her that it's YOUR business and not causing any problems. If she can't get the point, then she's not ready for a serious relationship yet anyway. Maybe she'll learn in time, but is it your job to teach her? People grow up when they are ready.
3) If you've got it all wrong and she's got it right, but you think it is #2 when it is actually #1... don't worry. You'll piss her right off and she'll leave you - which is fine, since you are the one not ready for a serious relationship.

A person has to be ready to own their individual problems.

or maybe she is hiding something from you?

Forgiveness vs permission is the key. But that has a limited shelf life as well.

Classy!

+1000 for just spending the time finding common ground and learning to live and let live. Fortunately my obsessive climbing thing is part of my charm according to the missus. Shelled out for a used double ledge and she didn't blink an eye, just told me to get it out of the living room once I figured out how to put it together.

Hiding shit is a good indicator that you aren't headed towards trust and comfort in your old age. Knowing that your significant other has your back in spite of your myriad failings is the foundation of long term happiness. And vice versa, I'd add.

Maybe co-op storage units so you and your friends could all hide your gear together. Get a single guy to put the unit in his name.

killis is right, but you're not just going to start a new day with that ethos, you'll have to work toward it.

in the meantime, don't be afraid to adopt the attitude of "being bummed out about the necessity of having to shell out the cash for gear even though you don't really want to because it's for safety and you're life depends on it."

wife (in a tone slightly sharper than merely conversational)- "what's that?"

me (as if there is nothing un-obvious about anything) - "what's what? oh that? it's that new belay device i had to get."

her (spoken as if to a three year old that she is reprimanding for the 10th time) "I thought you already had two?"

me (bummed out and dejected because life isn't fair) "well, I have my main one and a backup just in case, and the main one was starting to show some premature wear and I just thought that since my life and my partners life depend on all this dumb gear I should go ahead and replace it before it fails on me. I'm actually a little pissed because I had to go spend $30 on this thing. You know baby, I just really wish these gear companies would make stuff that lasts a little longer. But, you know, safety first."

You could also turn your bed into bunk beds for more room for activities.

sell her-think of how much gear you could buy with all that money.

climbing>girlfriend. ESPECIALLY the nagging kind that doesn't understand why gear is important to climbers.

The secret is to have climbing bring money IN. Make it a self-sustaining hobby.

Don't let a girl friend stand in the way of your happiness.

Find balance and harmony in your relationship by creating the opportunity for her to purchase or experience something in line with what we get out of climbing.
Might not have to be a ring- girls weekend on you? a new blender/ipod/whatever your chick digs...

That way you've got the ammo("remember that one time") when you really need it (see: new rope, set, trip to Thailand) but really, you're both getting your materialistic/recreational needs met!

If you can't hide gear purchases how do you ever expect to hide an affair?

Better hide your browser history when viewing the female climber pictures thread, too, brah.