I think you could do better if you look at correlations.

For example, if Alice and Bob always give the same vote, then their combined votes should be exactly the same as if the vote from one of them if only one was on the board.

Another possible improvement: Instead of voting yea or nea, you give a probability. If you give a higher probability, your vote counts more, and it helps you more if you're right, but it hurts you more if you're wrong.