Currently there's just the Possessed Tomb, Arcane Circle, and Gladiator's Arena (I think that's what it's called). Anyways. Two of those three reward Dark runes and materials, and the Arcane circle, despite clearly being a mix of Water and Fire enemies, only drops Water runes and materials.
Suggestion? Make Arcane Circle drop Fire and Water stuff. Then add more dungeons to focus on Light and Nature materials. And maybe some other mixed dungeons, like one for Light and Fire. Or Nature and Water. They're cool dungeons but it just feels like there's something missing with them.
Just remembered about the Beastial Maw, actually. But I don't even remember what that one drops because it's been so long. Anyways, my point still stands. We could do with more of these dungeons.