Well of course not. What happens is the water will be shallower by the sea wall than when it was first constructed. The shallower the water, the taller the waves.
I haven't been down on the seawall since before Alicia in '83, but IIRC at normal tide levels there was significant sand beach from the base of the wall to the shoreline. It would seem that additional sand would push the shoreline out even further from the base of the seawall, thus making the situation better rather than worse. In any case, a 20 foot surge is gonna be a real problem no matter what.
I will let you know for sure. I plan to be spending a couple nights on the seawall week after next ... god willing. I sure can pick'em when it comes to vacation planning ;^) At least the room rates are cheap.