Yes, if you have sufficient wealth and insufficient land, it may be worth saving certain areas. The cost can be extreme though, and it bears considering that the Netherlands don't face hurricanes, and 65% of their GDP is produced below sea level. What does New Orleans offer to justify such expense?
Yes, the levees should have been maintained, but why should it be Congress that does so? What does it benefit the US to subsidize a poor city location? If you want to live in a city locked in a perpetual (and now losing) fight against nature, why should the rest of the nation pay for your choice?
Yes, that's a cold-hearted approach, but with the majority of the population facing inundation over the next centuries, I think it's one that must at least be considered. In the face of the limited resources we will have to face the challenges that are approaching, if a city can't afford it's own salvation, is it really worth saving?