Although everyone who has thusfar been a cylon has just been very close to those in charge, but not an actual leader, and although Katee has said in interviews that she has been told she is not a Cylon and although Ron Moore made that comment about the last supper pic, there is always the chance that he was being deliberately misleading, or that he changed his mind.
But I don't think Starbuck is the final Cylon for other reasons (although I agree with everything else you say;)
At the end of Season 3, everyone feared and suspected she was a Cylon - how else could she have survived the explosion? - but that would make it too easy.
I doubt that the final Cylon will be revealed until the end and I don't think they can we can't sustain that "is she or isn't she" tension story-wise for the rest of the season - it would get old. Something decisive will happen to let us know she is human and someone else will be cast under suspicion until the final one is revealed.
I do, however, like the idea of the dead and rises again cylon-savior roslin. Or maybe she will be like moses, and lead them to the promised land but die upon arrival. Perhaps we can start a new thread that predicts who will be left standing when they get to earth, because it surely is going to be a blood bath at the end, don't you think?