Are you talking kinematics with the ground link? If so, the shock tower brace has nothing to do with that. The front suspension bolts to the crossmember which attaches to the chassis with rubber bushings. So if you're worried about suspension kinematic flex, replacing those bushings would do a lot more than adding a bar. I mean I guess they are tied together, but they're isolated from each other in too many places to make much of a difference.
It will help with chassis stiffness though, sometimes and to varying effect. And I guess if you're like Nash and the engine is hitting it and stopping the engine from moving when you get on the gas, it will help you put power down.
But for suspension stiffness, it's not worth it. Especially because I know a lot of the people have stock upper mounts which are probably old and a ton of other old, blown rubber bushings in their suspension which would be a better place to start if you want to get something more out of your suspension.
Here's a quick test to see if your shock tower bar will do anything. Take it off the car. Put one end in one hand and the other end in the other hand. And move one hand up and the other down well trying to keep the plates level to each other. That is the motion that the brace would see. So this just shoes that if it's a rigid piece, it will add a little stiffness, but it it's 3-pieces and has bolts attaching the plates to the bar, then it really won't do much. But even if it will do something, it's really not that much and the chassis iteslf is still going to be as soft as the weakest section. So even if you tighten up the front end a little, the center of the car could still be soft, especially with a targa.
