I might enjoy this sort of thing if it were added, but I think I would rather they put the effort toward something else. My reason for saying this is because to make these mini-dungeons workable with any group would mean making them easy enough to be done by any group. Logically, as you've already said, the rewards would be small as well. So if the challenge isn't there and the rewards aren't, what makes it different than doing solo content with two people?