Q:

Would the moon be brighter if it were completely spherical?

I remember reading Galileo's 'Dialogue Concerning the Two Chief World Systems' where Salviati and Sagredo explain how the moon would be almost entirely dark if it were a perfect sphere but after discussing this with a friend recently I wonder whether Galileo's argument might actually be wrong. 
If you follow the following link on page 69, Sagredo gives the following argument:
'If the moon were smooth as a mirror, only a very small part would show itself to the eyes of a peson as illuminated by the sun, although an entire hemisphere would be exposed to the sun's rays. The rest would remain, to this observer's eyes, unilluminated and therefore invisible'

A:

That depends on how literal you want to be.  If the moon were perfectly spherical, but the dust on top were the same, it would be just as bright as it is now.  
However take that to a literal extreme replacing the moon with a perfect sphere, most of the light hitting the moon would not bounce to your eye but would reflect based on the angle in which it hits.  It would turn the moon into a gigantic spherical mirror.  And as such, the sun's light would be represented by a tiny bright dot representing the small point where the sun's light would have to hit in order to reach your eye.  
It would certainly be bright but not much brighter than the brightest star in the sky, while most of the rest of the moon would reflect the blackness of space.  

