The bulk of the weight is due to using .095" vs. .065" chromoly, as well as additional bracing over previous bars. Keep in mind, I have not weighed the Targa brace yet, so until I do, we are operating on speculation.
Why the gussets? As each shock tower flexes, you see 360° movement, in a 3D plane. In other words up, down, forward, backward, side to side. There is not as much rigidity in the brace in a "vertical" plane, so the guessets are arranged to add a 3D bracing effect, as well as to further reinforce the tubing joints, which prevents further flex.
Experience? Pike's Peak is a great example. I overbuilt the hell out of the Pikes Peak NSX, which held up BEAUTIFULLY with a head-on collision with the side of a mountain. Because of the lengths I went to to brace, reinforce, and over-build the chassis, the car lives to race another day. If I would've built the car to "convention", the car would likely have been written off.
I carry the same attitude with these chassis braces. Why NOT gusset and reinforce the braces as much as possible? They are braces; make them stiff despite small weight or labor penalties. If you dont want the gussets, its pretty easy to leave them out.
In another note, that now makes two people interested in Coupe multi-point braces. Can we get a list going for these?