It made no sense for McCain and Palin to travel to Mississippi to get a briefing on the hurricane, or to take a tour - absolutely nobody in the path of the storm needs to be taking time to handhold political candidates for a photo-op.
Obama absolutely shouldn't travel to the immediate aftermath of Gustav, because it would be an utterly manipulative move. Rich Lowry, publishing a "reader e-mail" (which always read like botched column attempts), attempts to blast Obama for not going down to affected areas (presumably before and after, at least in the immediate aftermath). He can be briefed on the details of the preparation and response from outside of the hurricane zone, and he can view the damage - hopefully small - after the water's gone down. Celebrities, my friends, go make conspicuous and useless appearances in disaster zones so that everyone's aware of just how aware they are of how bad everything is.
The problem with Bush's response to Katrina wasn't that he didn't lash himself to a tree in the Fifth Ward and ride out the storm. It was that he didn't seem to be paying attention at all, and when problems were brought to his attention, he first denied them and then responded to them slowly and incompetently. People don't need to know that the President is right next door and has seen the house that's about to be destroyed. They need to know that the President is aware of what they're going through and working to help them recover and prepare better for next time. The fact that Sarah Palin stood where your credenza is currently smashed is cold - but charmingly down to earth! - comfort.