Regarding your second suggestion, "Potential loss of XP on downvotes"... I am opposed to any voting system which affects the voter differently based on the reputation of the node being voted on. Any such system will unfairly penalize either people who vote earlier, or people who vote later.

In the case of your suggestion, where monks lose XP for down-voting a node with a high reputation, monks are penalized for voting later. Why should a monk who down-votes a node soon after it is posted not be affected in the same way as a monk who casts a down-vote several days later? This would be an artificial and unfair system.

I lean towards allowing monks to use their votes as they see fit, and avoiding any complicated solutions which would end up creating new problems.