I'm dawnguard, finished the MQ done quite alot of the side quests, and the only time I had any trouble with vampire attacks was far outside riften when going to the cave to dawnguard when I first downloaded it.
I theorise that if you side with the vampires these attacks become more dangerous and frequent, which I think is completely fair and beth shouldn't do a dam thing about it, these are the consequences, anyway, there evil blood svcking vampires, why should you care if your fellow vamps are getting something to eat? If you wanted to be all lovey and careing, should have sided with the dawnguard.