Welcome to the GWOF & your RPM is probably fine. The key to good fuel mileage is to run below 3000 rpm on a 1500, should get between 35-40 running there but falls off significantly when cruising above that. I know you didn't ask that question but the info can't hurt a new Wing owner.
I would say 70 MPG would be about 3000 RPM'S. Your speedometer could have been corrected and is reading correct at 66 MPH. The Gold Wings speedo's are off by about 4 mph and at 70 MPH you are actually only going about 66 mph. So the last owner could have had a speedo healer installed on it.