In question 4012, Trey Jackson asks about the practice of casting down votes for all questions that are not your own. His question lead me to wonder about the current policy of allowing only one vote per answer. Instead of allowing only one vote, why not allow multiple votes with increasing cost? The nth time a user votes for an answer, whether up or down, it will cost m^(n-1) rep, where m is the number of other answers available at the time of the vote. (Or some other cost function). Using an exponential cost function will prevent high-rep users from becoming too strong, but this does give the high-rep user the ability to promote answers that are better (in their judgment).
(Note that I believe the first vote should be free, whereas m^(n-1) makes the first vote cost 1 rep; tweak as necessary, either by limiting the range or subtracting 1.)