My main issue would be (if I understand correctly), is a user with many accounts downvoting a post. Would the above mean that each account in the trail would carry more weight to bring the post down?

Many accounts downvoting a post wouldn't be a problem at all - because a downvote would cause the total payout for a post go down, which leads to more effective upvotes and less effective downvotes again (depending on how much voting power was used by the downvoter).

So multiple downvotes in a row would be become less effective with every downvote. From a voter perspective it really doesn't matter if you use one account with a large downvote or hundrets of accounts with small accounts - the result will always be the same.

Hope that was kind of understandable :D