Republicans and Dems have already made up their mind. They will vote for their guy or they wont vote at all.
There is also a sizable undecided block and these folk either will decide after the debates or they also won't vote at all. I feel that the Independents are looking more on single issues which will be addressed in the debates or they are the realy shallow folks who go for style, charisma and intelligence also brought out in the debates. The strength of the candidate is what effect the outcome as party faithful vote and independents come along for the ride. Which explains why we got smoked in 2006 we didn't show up as our candidates sucked.
As a result I read polls with a grain of salt. Lets not forget in 2000 Rasmussen, Gallup, and Battleground all indicated a sizable win for Bush.
The debates will be telling, then I will worry about polls.
Well, the drunk driving thing convincing a lot of conservatives to sit home could account for that. That said, there is a lot of difference based upon who is excited enough to go vote on the actual election day. I think the convention bounce does reflect a firming up in people's minds, and a growth or diminishing in enthusiasm. ...how meaningful that is for November is every bit as debatable as your post implies.