Actually, Obsidian itself might be a decent chest reward, seeing as it's a pain to mine manually and consumes lava to make it. That and a chance for Ender Pearls (Eye of Ender, Ender Lilly, etc.) would make me raid a complex or two at minimum. I would be happier to find an Ender Pearl than a Diamond, pre-end.
Edit:. I agree that spacing drops out amongst various structures would also promote exploring at least one of each, if only to see what they hold. If it's somewhat logical, it could help save time exploring the wrong places for the things you want.
Edit:. I agree that spacing drops out amongst various structures would also promote exploring at least one of each, if only to see what they hold. If it's somewhat logical, it could help save time exploring the wrong places for the things you want.