Ok, so we pretty much agree... these general election polls are pretty much worthless.
6 months is plenty of time, however sometimes polls come out right before a candidate arrives in a certain area. Those are the times when prepared messaging can't necessarily change - but it can be altered a bit via speeches, press releases, etc. Plus, a lot of the time campaigns will cover so many different alternatives to the main message just in case.
In regards to static direct mailers... most pieces are created early with look and feel and some sort of basic message. The copy will be changed and altered right up until the time it goes on Press.