I think there is value in seeing who promoted or demoted an idea. I am sure you know this on the back end, but sharing ideas and commenting on them builds a trust. If I see that the same jerk is always demoting my ideas, then I may want to take what he says or does with a grain of salt. On the flip side, if I see that a user promotes everything I would think that they are not properly using this system. As a user that is valuable information for me that helps formulate opinions of my idea exchange colleagues that will lead to a level of trust needed for any social network.