I believe Palin would have accomplished just as much even if she hadn't been picked for VP.
She was already a popular Governor and since there wouldn't have been ankle-biters to force her to resign, she would have finished her term and prepared to run for POTUS. The only problem is, she wouldn't have been vetted and the personal attacks would have done her in while they're out of the way now. Plus there would have been no book.
She wasn’t that popular a governor, people who weren’t GOP nerds had never heard of her. She might have been able to make a stab at POTUS in 12 as one of the crowd, now she’s a front runner and if she’s smart can stay that way. McCain advanced her clock at least 3 years, that earns him a little bit of “thank you” campaigning. Anyway, campaigning, even for a slug like McCain, keeps her in the spot light and a front runner in 12.