Regarding differences in mental imagery: only this winter did I really understand that good musicians have vivid aural imagination, while I couldn't hear any sounds in my head, period. Immediately after this realization I started exercising. By now I can hear complete monophonic melodies, and (on good days) imagine two notes sounding at the same time. Classically trained conductors can imagine a complete orchestral sound while reading sheet music. I don't see any reason why visual imagination can't be similarly trained.