When I read this, I immediately thought of the Space Era at the end of Spore. Ever played it?
Basically the idea is that having collectibles - such as lost pieces of tech, trophies, rare fossiles, rare gems, war mementos, etc. - give a purpose to flying around and exploring. Sure this might be just some old planet like all the others you've visited before, but rumors (or quests or a scanner) indicate that a rare item can be found here.
In Spore they were merely trade items. If you complete a set then the value skyrockets - something that might add to player economy or faction wars. In a game like Starmade, though, it might be possible to make the rare items function as placeables. That's an artistic choice, though, as it could easily clash with the voxel/cube graphics.
I like the idea of a holo-projector table. Kind of like how Display Modules work - a cube that you place that creates a graphic on one side. What if this graphic was a miniaturized ship, or statue, or object? It would still look and feel voxel, and still feel space-themed even if you find a golden crown or giant diamond. It could be used as a decorative, would tie nicely into quest systems, and be something that faction members are proud of (and want to protect).
I talked about an achievement system here:
http://starmadedock.net/threads/progressive-gameplay.6411/#post-91933
