yes, mission boards, derelict wrecks to find with experimental weapons you can affix to your ships, etc. something to drive the player. if you just drop a new player in the sandbox with no direction, they tend to lose interest pretty quick. without a reason to explore, the player in my experience often doesn't bother to. take X3, they have secret gates, derelect wrecks that can be salvaged, alien systems, missions that sent you far out. there were reasons to go out there and explore the universe.
minecraft is the most recent example i can think of. you could explore, but after about 15 minutes, you realize theres nothing out there to find, and you come to the realization that exploring further is pointless, because you wouldn't find anything. now compare that to terraria, also a sandbox, their exploration would yield treasure chests, underground jungles, magic items, floating islands, dungeons, the underworld. all of these gave you incentives to expore further and further from your base.
take spaz, i can't immagine anyone would bother really going around the systems if there wern't different items to be purchased in different systems. without that incentive they would just blitz through the story missions.