Personally I don't vote on AM nodes for this reason - it seems a bit of a wasted vote.
Why is it a wasted vote? Do you believe a vote is only worth something in its ability to affect the XP of a node's author? If you are voting to change the author's XP, how large a role does the author play in your voting decisions? It is best to vote on the content of a node regardless of who the author is. A vote on non-anonymous post may have a relatively small chance of causing a change in its author's XP anyway.
Regarding your idea in general, as others have pointed out, if we do this, we might as well display node rep all the time (or make it a user setting.) While I'm not entirely convinced that would be a bad idea, I do understand the arguments against it. In light of those, I still support the addition of an abstain option for people who chose to never vote on a node.
-sauoq
"My two cents aren't worth a dime.";