Honestly the lower braces will make a pretty huge difference. They are defiantly worth doing. Any stiffening of the car makes a big difference.
The more you do, the more weight you add, making weight > power in the current ratio. But you prolly won't need to / want to, but for anyone else who comes across this, you can weigh the braces before installing them.
When you can write that down somewhere, and take things out you don't need (if you use it competitively), and weigh each thing removed, add them up and get back to the original weight before the braces were added.
^This might be a given to some, but not all.