Unknowable. Steve Schmidt says yes: she brought more of the base out than McCain ever could have. Much research says no, and that she probably deprived him of 2 percent of the electorate. We cannot know for sure - there are no control experiments in history, as Matt Continetti concedes (while breezily ignoring his own view).
My hunch is that she did indeed bring out some of the base that otherwise would have stayed home, and may have helped fundraising - but she may have lost many more moderate Republicans and Independents to Obama than, say, McCain's first choice, Joe Lieberman, would have.