How is it that you or I can know what answers the OP finds enhance her understanding? How do you know what responce the OP finds more clear?

I would note that merlyn has stated before that different people think differently. And a method that one person finds natural to think about a problem and find a solution could be entirely forign to another person.

I think the guidline for neither ++ or -- is to remove the 'well it wouldn't help me so it's worthless', from the equation. If we move to '-- if I don't find worth in the responce' we could effectivly punish (no matter how often any one says node rep/XP doesn't matter) a poster that stated the same information differently, no matter how slight, that was the post that made it 'click' for the OP.

Chances are a late post like that would not recive many ++'s any ways. So to make the policy go and -- would discorage what could be deserved ++'s further, causing a what may or may not be a more valuable node to go negative.

My personal rule for voting on SOPW is that no responce but a blatantly wrong (not just minorly mistaken) responce, or an outright dangerous responce is truely harmful. While a late responce is likely not to be as helpful and there for less likely to get a ++ from me it is not worthless or harmful. The one exception might be an almost direct copy and paste replied to an earlier post so the threading places it on the page before the original. But dispite your title I never see your guidlines address plagerism vs. simply similar posts later in a manner satifactory to me.