The first planet that comes to my mind is Risa. Its a beautiful beach paradise world. It has lots of eye candy scenery, people, props, etc... but zero interaction. Adding quest npc's and storylines here would rock. Some quests can be local, some intersteller. Perhaps puzzle solving quests that have vague clues that add up to an epic sized treasure hunt for ancient buried technology or rewards. Other planets that could fit this type of gameplay could be Vulcan, Earth, Betazed, Denobula, Andoria, Bajor, Cardassia, etc, etc...
I am thinking very VERY large outdoor/indoor type areas. Perhaps 10 times as large as the current Risa playable surface. Each becoming its own little community with vendors, quests, plotlines, mysteries, and of course the eye candy we all have come to appreciate in any alien world of wonder. Perhaps even adding purchaseable buildings that fleets can use and call "homebase" that are accessable only to members of that fleet. These are just a few thoughts. Some folks will undoubtably flame this apart claiming its copying other games somewhere, or some company tried this somewhere... but whether or not its been done before in some galaxy far away or near does not matter.. its still fun, interesting, and adds just one more avenue of play to any growing community.

Sounds great, but Risa really needs a NIGHT cycle.