There is no comparison to the American quality of life between the pre Reagan and post Reagan administration. Smart liberals know not to bring that up. He "ended the cold war without firing a shot." And reinstalled pride in being American.
About Palin, Democrats are going to shoot themselves in the foot if they go after her. She has more experience than Obama, and is a proven reformer. Biden is a life long politician. So I think its going to be harder to sell the "change" message from now on.