I totally agree with you. I'm just not willing to speculate on what shape the doubt will take. Once that becomes clearer, I will reconsider the race. What would be nice is a poll, even a partisan poll, to give some inkling of whether the electorate has changed.
Although southern Louisiana was of course ground zero for Katrina, the really hard-hit regions were either sparsely populated (e.g., Plaquemines Parish, which is politically inconsequential) or not in Melancon's district (e.g., New Orleans). Now, I don't know how the rebuilding has progressed in LA-03, but outside the urban centers I would think things are more or less back to normal in terms of population. My guess is St Bernard Parish is probably the only area with any significant population that might factor into the political equation.
And finally, from what I've gathered, Melancon's role in the whole Katrina mess was well-received.
The majority of the damage went to LA-01 and LA-02, so I don't know how much Katrina will alter the overall demographics of the district. I imagine the impact would be minimal there. Since LA-03 was not as badly damaged, voters might pay attention to other issues, though I would agree that Melancon was one of the few that did not come out looking bad (unlike Blanco and Nagin).
There are genuine vulnerablities that Romero can hit on in Melancon's record. Melancon is a class warfare politician that votes against tax cuts and building oil refineries if it benefits "the rich." He is defintely no Billy Tauzin.