Looking at the reputations of nodes I've voted on in PerlMonks Discussion, I'm not seeing many downvotes*. Granted, it is a small sample.

Your suggestion is interesting, but I like simple systems and I'm not sure there is enough of a problem to make things more complicated for beginners (In addition to a bunch of voting/exp information to learn, new users now get thrown for a loop when they look at PerlMonks Discussion. I'd expect periodic SoPW questions and/or "Possible Bug?" reports about this).

Also, why worry so much about experience/reputation? It is, after all, just a number. Another way of thinking about it is, if your suggestion has attracted a flurry of up and down votes, you have struck upon something worth discussing :).

* - Not counting nodes with questions that have been brought up a bunch in the past, those collect downvotes pretty rapidly.