Well i don't think so that the campaigns will lower their rates because these rates are running from many months no matter what is the price of bitcoins . I would say that the rates of campaign per post are universal rates So we will not see any change .
But ive seen some campaign starting to close down maybe they are affected to it and others really lowered their payments because their payments are based on USD and thats totally ok as long as they will continue their campaign and we are still payed.