i would say its a good idea to replace all four... while your are it.
but braking is more front bias, so you MIGHT be able to get away with it
hop onto DBA and check the pdf they have for NISSAN, find out the standard width it should be for your 33 and see how much you have left for both front and rear rotors.
This should give you some indication of how much meat is left on the babies.
Eug