As a rule of thumb, you need to replace the rotors every other pad change. Pads avg. maybe 35k mi. so at 70k mi. you're likely due.
Or you can use a micrometer and check their actual thickness. Rotor wear limit for the Base model is:
- Front 22.0 mm
Rear 18.0 mm
For the 'S' model :
- Front 26.0 mm
Rear 22.0mm
If you don't own a micrometer, a cheap plastic vernier caliper (available at any Lowes, Menards or Home Depot for <$10) could be a substitute (though a less accurate one). Just be sure to take measurements at several places around the Disc and account for any 'lip' which may have developed from wear.
Finally, if your discs just make the limit, but you're replacing the pads, replace the discs anyway because the new pads will quickly wear the discs below the minimum and reduce braking effectiveness considerably. Like it or not, discs are a consumable and part of the price of admission.
PS Be sure to flush and replace the Brake Fluid if it's been 2 or more years, in a climate as humid as New Orleans, that's the maximum I would go w/o changing it (which also happens to be the maint. spec.).