There is a story line being peddled by some that the Dems are squandering their convention by not hitting the Repubs hard enough on policy differences. I personally take the opposite view. I believe the Dems are very wisely utilizing their convention time to shore up areas of weakness / perceived weakness. In an election where all of the fundamentals are going in your direction and you have a dynamic and likeable candidate, that is really all you need to do.
Obama's campaign essentially has three main problems: One, a perception that he is not patriotic enough / too foreign / too weird to be president. Two, a handful of core partisans who are not yet fully on his team after a long and emotionally charged primary. Three, a perception by some that he is not strong on foreign policy / defense issues. You could also add in a fourth / bonus issue, common to all campaigns, that you need to sell people on why you are better than the other guy.
Obama's folks are keenly aware of these weak areas and are utilizing the convention to brilliantly shore up these points. You have a perception that Obama is an elitist, radical, you bring out his wife and kids and show how human they are. You have a problem with part of your base not being fully on board, you have his major opponent come on and say she is on board with him and beg her supporters to be as well. You have a problem with the perception that you are weak on defense issues, you have the extraodinarily articulate and likeable former president and the extremely knowledgable VP candidate come on and lay out your vision for foreign policy / defense. You want to sell your candidate vs. the other guy, you have that candidate, who is likeable, smart, funny and focussed, come in, with his brilliant speachification, and tell you why you should vote for him, laying out in great detail the differences between him and his opponent,
You have four problems. You have four nights. You have four themes. You use those four nights to solve each of those four problems.
Lastly, there is a reason why the dems have been trotting out local officaials and down ticket candidates to jab at McCain. These folks are going to get tons of free local air time. It's like free paid advertising.