How much for 71 Thermoquad?

I will give you my opinion, & I have no proof, just like you it seems.

I doubt there would be any discernible difference in the operation of the primaries only between both types; no difference the butt-meter could feel or a dyno could measure & same fuel usage.
With primaries & secondaries operating, I believe the 71 model would make more measurable hp because of the design of the sec discharge tubes, which were copied from the Comp Series TQ.