Changing tom heads

In days past, whenever I busted a tom head or one just went dead on me, I'd change all the tom heads instead of just the bum one. Well it happened again the other day. The upper ply on one of my hydraulics sprung a tiny little tear. Normally I'd just change all 4 heads (they're all about 5 years old) but I'm being more budget conscious and thinking of replacing just the broken one. What do you guys/gals do? Change just the one, or all of them? Would one new head not mesh well sound wise with older broken-in heads? What do you think?

Changing tom heads