The polls did show that most independents were not positive on Palin. That was not surprising due to Fey's characterization of Palin which had a significant negative impact. However, most of those independents were going to vote against McInsane anyway.
It would have been theoretically interesting if McInsane had selected Lieberman on the ticket, but I suspect the results would have been the same except for losing some conservatives and gaining some independents.
The main reasons the GOP lost were 1. McInsane and 2. Bush.
I agree with your assessment completely.