Hm,
curious enough you just care about downvotes. I don't feel that the use of downvote power should be in any way restricted. And it should not be made public as well.
What is so bad about people downvoting nodes? Even if the node would not have deserved it. If there is someone who just downvotes because of likability he probably won't be a very high-level monk so he won't have much votes to spent.

I'd just leave it to overall statistics to get the "real" value of a node. If there are enough people in this place it will all come out well.

On the other hand: I see that voting bots could be a problem and the "show-me-your-rep" vote is something I have to admit I used sometimes (though I usually ++ that node then). Thus I encourage the null-vote button. For the problem with bots I can't offer any solution besides some weird and not thoroughly thought through thoughts (I think I need to be punisished for that english, er what? *grin*) like measuring time between loading the node and hitting the vote-button or check for "randomness" or something. As I said, just a faint glimpse of an idea...

Let people downvote as much as they like to without punishing them in any way, it's just another side of this fabulous community.

Update: fixed a few typos

Regards...

Stefan