That's very true, and lots of good people are helping to do just that -- outside of NO. But the question remains: if the gov and private sector are going to rebuild the city, ought it simply be returned status quo? If not, why not try some innovations?
Well, if the roof of your house is missing, you dont spend your money upgrading the kitchen.
If anything, a "city of yesterday" (more agricultural land) would be more appropriate, and Katrina already has taken care of starting that. Areas will be abandoned and perhaps farmers (high-tech or not) will take advantage of the dirt cheap land.
I like your idea but perhaps it combines both elements yesterday and today. In other words, a much smaller city area, more elevated and protected, and a much larger plowed over farmland/floodable zone encouraging kelp farms or those things you suggested.