When changing brake pads, is it "always" necessary to resurface your rotors? Also, if you use the cheaper "non-metallic" brake pads as opposed to the "semi-metallic" will it reduce wear on your rotors?
It is not ALWAYS necessary to resurface the rotors....but it is usually the best thing to do. If you don't, you run the risk of surface imperfections on the rotors ruining you new pads. Most rotors NEED to be resurfaced before installing new pads. The only exceptions to this that I have seen is when the pads being replaced were defective and are not very old (and the rotors were resurfaced for them). It's not usually very expensive to resurface them. I used to take mine to NAPA and it cost about $15-20 apeice. Drums were cheaper.
Of course it depends on how much "meat" is left on them. If you don't have enough to have them cut, you should replace them.