Well, I highly doubt Dawn will be the only target, lots of victims to pick from, and going after them is less likely to get an irate Slayer on them, as opposed to going after Dawn will. I mean really, a GOD decided to mess with Dawn, and got her head smashed in with a hammer for her trouble. I think Dawn has a big invisible sign over her head in Sunnydale, telling the various baddies not to mess with her. There are some benefits to being the Slayer's sister I would imagine.