The price per KW of SPS

>My main problem with the integrated-solar-cell-and-solid-state-microwave-emitters proposal is that you can either point your solar array at the sun, or your transmitter at the Earth, but not both at the same time.
>

Actually you can. The phased array antenna can point the beam towards any direciton in a hemisphere, even if the surface of the antenna is not normal to the target.

>I've seen designs that added mirrors to increase insolation on the PV, but they strike me as a Rube Goldberg solution to the problem.
>

The SPS mounted mirrors I have seen are for a different reason.
They are not even steerable.
Typically they are for GaAs array (not for Si) which can run at a higher temperature. Because mirrors are cheaper than
PV cells, they are used to insrease the collecting area.

You cannot do this with Si cells because they cannot withstand the higher temperatures.