I think the answer is much more simple. A door that's going to hold something they didn't find useful is going to more than likely be a better option for a choice. I don't trust that the Malnosso would leave behind important information, especially if they had time to move everything out and lock it up as tightly as it was.

But since the card did exist, I do believe there's something of value down there. More than likely weaponry. Something that if they needed to access it inside the barrier it would help against any attacks from the Third Party.