I have 82k on my 09 RTL. Rear pads were down with maybe 15% left. Front pads were close to 35%. Last year they (a ROC business supporter) ran a special on drilled and slotted rotors with ceramic pads. I bought a full set. My wife's 09 Accord last week developed this weird hum when backing up. So I checked and sure enough the rear pads needed to be replaced. So I quickly did them and then my MM on my RL hit 10%. So I decided to do the brakes while I had all the wheels off for rotation. I will keep the rotors as they are in excellent shape, just incase I have a problem down the road.
Yes the magnet is for the speed sensor. I almost forgot, because the fronts are in the hub, which I just thought the rear were too. Glad I caught it.