Optimism/pessimism and election strategy...

Reading the thread on the DNC, a thought struck me: the Republicans, by very dint of their basic outlook and strategy, must paint a pessimistic picture of the current/future state of the U.S. under President Obama. This is, of course, natural and basic; how can they make an argument for replacing him otherwise?

This sets up one side as coming off a lot more optimistic about the way things are than the other. So I was thinking about the perils here of coming off as either out of touch with the hard realities of the day, or so “doom and gloom” that it brings voters down.

Which side has the edge here, if either, in this regard? How can they best massage their messages? What effect will this delicate balancing act have on November?