Those are all valid points. On the point of it being from an “ethics charges” angle they (Obama camp, debate mods) may just play the generic “can she take the heat” angle.
If you look at the Palin polls through the summer, you can see the damage her resignation did to her with Republicans. The opposition didn't like her to begin with, but her resignation did damage to her with many Republicans. Whether or not that damage is lasting, remains to be seen. But, suffice it to say, American don't like quitters. And, Americans generally draw a distinction between people who quit one government job to "take a promotion" at some other level of state or federal government. Palin did the former, not the later. It will hurt her.
I agree wholeheartedly with many of the other things you've said, and would add this - 2008 was a "bumper sticker" election. Americans heard a guy with soaring rhetoric and some great bumper stickers - "Hope and Change" and "Yes We Can". Now, many of those same voters are having significant buyer's remorse because Obama didn't provide specifics, and the electorate now realizes that they should have demanded some specifics - as always, the devil is in the details.
I think if America is willing to fire Obama (the known quantity for the unknown quantity), they'll be more likely to so because of his opponent's ability to articulate the details of a compelling and reassuring vision. Maybe Palin can deliver a message of vision, but it remains to be seen if she can speak with specificity about issues and ideas in a way that people find engaging, compelling and in a manner that says to voters that she's a genuine policy expert - very much unlike Obama. That's going to be a problem for a woman who's such a poor and wondering extemporaneous speaker - she has her work cut out for her.