I think you are exactly right. At the moment, 40 million people think she's great. Even more will do so, among those who missed her speech, after reading all of the positive reviews and by word of mouth.
The Democrats have to try to smear her indirectly, through the media, before they can gain any traction. And even the media has to be careful, because all of the vicious attacks which preceded Sarah's speech definitely caused a backlash with the American public.
They will go more subtle for a while: tell lies by omission, distort small things, show the least flattering pictures, play the least commanding sound-bites, look for negative testimonials they can slip in here and there. Meanwhile the heavy investigative journalists (the people they should have sent out to begin with, instead of US Weekly) will be digging for all their worth.
They'll also do a huge expectation build-up to the Biden debate: it will actually look like it's positive to the naive observer. Then if she has a so-so performance they'll unload with talking heads who announce that the lack of experience was "really on display." If she has a great performance, they'll be able to say, "about what we expected."
We can handle the twits at the Networks. Ask Mary Mapes.
Ll the vicious attacks certainly increased her audience to way above what it would have been if they had not panicked.