The other issue is that when sailing hard on the wind, the luff of the sail tends to deflect quite a bit from the vertical, much like a genoa luff will if the headstay tension is too soft. Knothead might be able to comment further, but I think that a fair bit of deflection is inevitable because of the nature of the beast.
John, You are exactly correct. No matter how much you tighten the wire, there is really no way to prevent the deflection of the luff. And the problem that I can see with the CDI system is that when the wire is tightened all that load is transferred to the fasteners holding the bracket on. As I said earlier, there is a stronger way to do it by modifying the gooseneck and bringing the wire down to a proper termination like a tang somewhere below the boom. But you will still have a lot of deflection in the foil.