Well, she can start raising money for her campaign for one. Two, she can start putting together signatures for the states that require thousands and thousands of signatures to get on the ballot. Three, she can start building a 50 state campaign infrastructure.
Tell me one benefit of waiting until the last minute. And keep in mind that "tweaking the media" is not a good reason.
Unless, of course, she is going to run as a 3rd-party candidate, which I won't rule out. I actually find it more likely that she takes that approach than she declares as a GOP candidate. If people want anti-establishment candidates, Ron Paul has already declared for the race. I don't support him, but I don't recall him campaigning for John McLame and fundraising for him in the AZ GOP primary.
Unfortunately (depending on how you look at it) a lot of people just don't see or understand the campaign strategy Palin is employing.
It's really not rocket science. She's got 100% name recognition, which means that she doesn't have to campaign for as long as others who need to establish themselves, and get the face time required for the public to make a judgement about them.
While the others are in the middle of the field battling it out with each other in the demolition derby, she's outside the ring, taking on no damage and conserving hers and her supporters' resources for the real fight ahead.
In the meantime, because she's established alternative lines of communication with the public, she continues to get her message out to the people. Today's speech is an excellent example of that.
The demolition derby of the early primary is a fight that she is wise to stay out of. There is nothing for her to gain by being a part of it, and lots to lose. When she does step in, her opponents will all be broken and bloodied by the previous months of the contest, and some will have fallen by the wayside.
It's not costing her a thing, in terms of public relations or capital (human and otherwise) to stick it out until the last possible minute. Her supporters aren't going anywhere, and she doesn't need the big money donors and professional political operatives to gain all the benefits of running a winning campaign, while unannounced.
Brilliant strategy, if you ask me.