the problem with old bindings is that you dont know what the insides look like. in essence they're just big springs. if the previous owner didn't back the DINs off during summer or had them set on 12 the whole time they may not function as expected and you could get hurt.
i dont know about you but id be fcuking pissed off if i decided not to spend $200 on a pair of new bindings then did my knee and limped for the rest of my life.