I disagree with the premise. Each person has the opportunity to vote on a node one time. There are plenty of people circulating around the halls of the Monastery that a good post will receive plenty of positive votes. What you're proposing would only contribute to vote inflation (devaluation of a single vote). A great many of us never manage to use all of our votes. If we suddenly had a means of using two votes on a single node that we happened to like, a lot more votes would get used. The net result is a devaluation of the single vote.

Great posts already get enough votes. It's more concerning to see flat out wrong posts getting upvoted marginally; that reflects that some voters just don't even know what they're voting on. But that's a completely different issue. It is, nevertheless, an argument for restricting the vote to one per person per node.

I'm not trying to say there haven't been times when I've wished I could throw a whole bunch of positive votes at an unusually high quality node. But the fact is, that node still manages to attract a whole bunch of positive votes, one vote at a time. If I personally feel strongly about a node, I'll take the time to send its author a /msg thanking him/her. I think a little of that goes a lot farther than a few votes.