|Don't ask to ask, just ask
I agree that the 'tension' indicator would be a good idea if it were visible before you cast your vote. And I prefer your simplified method of deriving it. But, for nodes where you can see the reputation (nodes you wrote, or nodes you've voted on) why not just show the total upvotes and total downvotes? What better 'tension' indicator can there be?
As for people getting all worried that the votes on their nodes have not all been positive, wouldn't showing the total votes cast help to minimize the worry?
I would bet that even some of the Best Nodes got some downvotes. Surely, someone clicked off a -- on some of those. If not on the Best Nodes of All Time nodes, certainly on the Best Nodes of This Week nodes...
Seeing that 'it happens to everyone' might make the occasional downvote less painful for those whose self-image is tied too closely to their current Perlmonks XP value.