Current resource rooms require level 500 to access, or to attempt opening at least. There are currently two empty rooms to the right of the current resources that are currently not in use.
What about jade in the next room? Hobbs mentioned before (I'll have to look for the post) some possibilities about rough jade and refining to a refined jade. This would of course open up additional crafting options. Maybe level 750(?) needed for this room.
EDIT with Hobbs' post: viewtopic.php?f=4&t=15369#p95110
For the last room how about titanium? Or maybe adamant? More crafting options, perhaps with some refined jade and magic gems? This could be maybe 750 or 1k for this room, but...
The last resource room would have stairs to a lower level. If the room itself required 750 this would probably be a level 1k requirement for the stairs.
This would lead to... the HGM catacombs! I'm not sure what all would be down here, but for those who wonder where ancient worms come from, well, ancestor worms or ghost worms would lurk in locations down here. We all thought Hobbs was sadistic before, but think of a second level he and the others could play around with!

Much thanks to LK and a fun conversation we had earlier!