Open World Radio Missions
They should reward Ren/Exotics, very small amounts though like 10-25 Ren or 5-10 Exotics. Add resources to the workshop similar to the seeds for the plants. 100 wood/stone/etc for some amount of Ren. Add an orbital store, via the orbital exchange interface that allows you to "order" supplies from the station for Ren/Exotics and have them dropped in on a pod. Give them a faction, but make the reputation with that faction matter, better rewards/missions for grinding higher rep.
Other than the new fruits and vegies, the only value I've found in these is the occasional tower mission that gives me a free beacon (I destroy the tower after the mission completes and have the free beacon, they are too expensive otherwise).