Everyone has their own opinion on rotor replacement and both sides can be argued. My thoughts are that when you're dealing with an unknown and the parts are relatively cheap, it's best to replace the part. This goes two fold when dealing with brakes.
Your rotors should have a minimum thickness stamped on them. At a minimum measure the thickness to see where you stand. The fact is that those rotors have been used through at least one set of pads, maybe more. I'd hate to see you replace the pads and then have to pull it all appart again in 5-10k miles and replace pads and rotors because your rotors warped.
I see this much like changing your oil....preventative maintainence.