I would like to see the first feather Palin adorns her cap with be campaigning for Republicans in 2010. If she can be instrumental in shrinking/eliminating the Dem majority, it would demonstrate her effectiveness in winning a national debate.
The Dems need pounded mercilessly on unemployment, wasteful spending and the destruction of the free market.
At the rate the mushy middle is already abandoning Obama, the task is eminently doable.
It actually would do three things:
1) Show signs of a "sea change", i.e., swing the momentum back away from the rampant socialist train wreck we're on. It's not enough to do the typical "squishy" Republican tactic of "the same as the Democrats, only not so much" (I'm looking at you, Romney).
2) Establish Palin as a legitimate force to be reckoned with, including having a fairly visible platform to "rehabilitate" her image. The fact is, I believe her current negatives are the highest they'll ever be; as she goes on the offensive, she'll be able to erase many false impressions and doubts. Of course there's a core subset that will always be opposed to her, but not enough to defeat her if she can address the ones who can change their minds.
3) Provide Palin with the "ground troops" she'll need to win primaries, and eventually, the general election. Individual candidates and state parties that gain because of her influence will be pretty much compelled to return the favor. Any candidate needs that organization (c.f. the failures of the Thompson and Hunter campaigns in 2008), especially in the primaries. With Romney as her prime competition, she'll need to match or exceed his organizing abilities. Even if someone else steps forward, preparing to take on Romney will still leave her with a solid organization to deal with other contenders.