Do more adv. marketing centers on a planet = more benefit, or not? I seem to recall reading someplace that certain buildings did not give you any benefit after the first one on a given planet was made. Did they ever fix that?
Also, if a planet falls within the radius of more than 1 starbase, does it get a benefit greater than if it fell within the radius of just one? Should I be honeycombing my star systems with beneficial starbases?