The way I see it, if there's lots of traction, you would use the ALU braces. If the track is rutted and blown out (bumpy) use the composite braces or even with the torque rod in the front and composite in the back. When you want more traction, use the composite braces.
When it's really bumpy/blown out use the composite braces. If you already have lots of traction then run the ALU braces. When there's huge chassis-slapping jumps, use the ALU braces. Tight tracks would favour composite. Big flowing tracks would favour the stiff ALU braces. But that's being over-simplistic. Ya just gotta use trial and error. See what works for you.
As for the composite braces holding up, you got no worries! I'm sure they will sufficiently brace the buggy. Especially with the quick change mount. I don't know what would happen if you removed the rear brace. I've read Yannick runs without any rear brace. Yannick also gets free parts! So even if he tweaks the heck out of his buggy, he can just get another chassis. I think someone else mentioned not using a rear brace. AJoiner? Maybe he'll chime in too.
I've just relayed what I've read - and been told - the way I've comprehended it.
Last year I ran the same braces all season so I can't really say for sure how the buggy will react. I'm gonna mess with braces this year for sure! 
regards
speed metal