For the most part, I put all my functional old sticks in a drawer. Then, as they pile up, I try to make decent pairs for gigs.
I like having nice sticks for practice, since I think its important when practicing fine stick control and what not.
But, I can use beat up, mismatched pairs for rock gigs since the beats aren't really that hard. I've never been to a show where I criticized the drummer for imprecise, unbalanced rolls... Plus, its expected that you'll break sticks when you're playing rock, so it adds to the effect.
I am a firm believe that if you practice enough your body will adjust to mismatched sticks enough to play easier styles well. So waste not, want not.
Also, I let my students play with my unbroken but old sticks sometimes. It lets them experience different sticks without having to explain to their parents why they need to go buy new sticks when they still have perfectly good ones. This is especially true with specialty sticks.
And yes, when I play more complicated music or even more difficult styles of rock I do use nicer sticks.