When you say "wave screen" (concrete) I think you really mean the rock breakwater.
There is a big wind shadow in front of the wave screen. You need to be at least 100m away for reliable planing even with a kite high and riding a raceboard.
There is not much room for racing and no good spot for spectating except for the beach or peering through the bushes on the cliff.
In previous years the RS-X racing has been off the breakwater. There's heaps of room and heaps of wind. People can sit all along the breakwater or stand in the deck or in the bar of the yacht club (members only except for the restaurant).
They usually set the course out to sea from the buoy off the yacht club, opposite the control tower. That's probably good for racing but not so good for spectating (unless you're in a boat).
The view from the beach is not so good unless they send competitors down towards Green Point. Then you have heaps of parking and good viewing/access from the beach, cycle track, cliff, road etc.
The wind and terrain towards Black Rock is pretty good but parking and viewing from the road is restricted. There's a few reefs that will take out raceboard fins if they come in close.
PS Some of my most fun kiting is chasing the women's RS-X racers around the course on my kite. I could cut the corners and beat them to the marks. Plenty of action and hot women in wetsuits.