I made a very sturdy steel strut brace for my old coupe. Could not feel the difference when I fitted it at all - either before or after the cage went in. Its the only "suspension" mod I've ever done that had zero effect. And I've done silly little things at the track like loosening rear sway bar link pins 2 turns to help correct an oversteer problem - and you can notice something as small as that!

Strut braces? can't hurt, but probably don't help much either!