On the suggestion of someone else on the forums, can't remember who or where sorry, we tried two Adventure decks in last night's game and it worked great! We usually split the deck in half, then someone picks which half to use, then maybe we actually get through one half. Using two, we actually knew that all the cards were in play and there was a possibilty for everyone.
What I'm wondering about is the ramifications of doing this. This beefs up the Sage's ability, and frankly he needs it. Also the Dark Denizens, and the Highlands equivalent, where you put 3 Dungeon cards on the Adventure deck, we would double that up for both decks. I don't really see a drawback here, it just makes them a bit more pervasive. Is there any other consequence that I might be missing from doing this?