Why a 3? If a story is so not what you like that you cannot finish it then surely it is a 1? If the lowest you can think of giving is a 3 what are 1 and 2 for? From what you say, 5 is for stories you like and 4 is for those you don't much like, and no vote is for anything you really don't like. This means that your votes tell the author almost nothing, since (s)he is not aware that you have [started to] read the story if you don't vote.I... I never vote on a story that I cannot finish - that rates a 3. ...
As I have said before, feedback is much more important than votes, especially since most people only vote 4 or 5.