I never noticed the resemblance of the rubber ball to the planet.
Early was a great character. Whedon has said that he'd planned to have Early show up again somewhere.
The comics vary greatly, I was pretty disappointed in the Shepherd Book one. There is no way it told us the story of the man who Jubal Early says "that ain't a shepherd" about, the man who got instant medical treatment from the Alliance.
I caught "The Message" again yesterday on SCI, and noticed something else about Book. He seemed to know a lot about Womack, his training, and his jurisdiction. There was a lot of depth to the Shepherd that we never got to explore.