I've thought about this too at one point, but the UCA sees way less forces than the LCA, which also needs to absorb braking forces.
Bracing a LCA is done quite often and I've done it myself too, but I do think the plate that is being used is way too much material and weight for the purpose.
IMO a fairly simple X-brace on the bottom should do the trick here.
But if I do wanted to brace an UCA, I would probably use a piece of 1/2" ΓΈ light tubing with a bend in the center so it touches the sides and the center part together.
