I think it would be nice if there were artifacts that give energy - but only a set amount of points. Like an artifact giving 20, 50, 100, 200 energy - but not filling to max energy like the energy cube. They could be harvestable from artifact points (if they were weaker ones), or found on NPCs - and would just provide a small boost. They would still help with doing missions and leveling. Or you could just have them fill 25% or 50% of a ship's max energy if possible - so they would provide a greater bonus to higher level players and make them more valuable.