I can't speak to the specifics of wheel offset and how to calculate and compare that to the wheel spacers. However, the guys at Slee Offraod (where I had my Spidertrax installed) explained it to me in layman's terms that running the wheel spacers does no more or no less harm to wheel bearings and other componants than running an offset wheel. So, if you are running a wheel that provides the same offset as the Spidertrax would to the stock wheels, it would be no different. I know that is probably not much help but I hope that helps put it in perspective.
From what I understand, the TRD wheels provide enough offset that they should look flush with your fenders on the 4R. You probably don't need the wheel spacers in addition to the TRD wheels.