[GraemeL]

You're probably correct, but I also have know idea how much of a difference it would make.

One other advantage would also be the lack of atmospheric scattering, but they have made huge strides with adaptive optics so it might not be worth the extra cost of getting all the components to the Moon and assembling them.

You would also be limited by how close you could point the telescope to the Sun when it's in the sky. I think Hubble isn't allowed to point closer than 50 degrees for fear of damaging its optics/sensors.