The end result still is that she ultimately bumped him up in the long run. McCain had been trailing the entire Summer and was down 15% points in July (before the RNC). After the Convention on Sept 1st, McCain got a bounce to the other direction was leading by 10% points. Although it did not stick, he lost the election by 7% which is much better than he would have done without bringing in Palin's electorate. Love her or Hate her, she ultimately helped him. McCain was just that bad of a candidate. It ultimately was his own fault he lost being the neocon and dry person that he is.
Maybe, maybe not. She definitely gave him an initial boost. Her favorability rating right after her RNC acceptance speech was higher than both Obama's and McCain's. But then she experienced drastic drops in those favorability polls after her Katie Couric interview, after the Biden debate, after negative press, etc. Some of the polls indicate that, at times, she would lose 10 points in a matter of days. The electorate that she had initially brought in were losing faith quickly.
Had Palin maintained higher polling numbers, McCain might have won. But she didn't, and a large part of the reason why she didn't was her own fault. McCain's campaign could have changed the manner in which they prepped her and handled her in the press, but ultimately, her own inexperience and lack of political knowledge (and the media's attention to these flaws) were the largest reasons for her downward trend in the polls.
With that being said, sure, she gave McCain's campaign a boost that it may have not otherwise seen, but then she also dismantled that boost to a very large degree, if not entirely. McCain was not a great candidate to begin with by any means, but his campaign showed signs of potential success with the initial addition of Palin based on polls. That glimmer of hope faded as Palin's shortcomings came to light.