depends on your definition. I can't say with any authority the trunk cage does anything. I believe just putting in the top bar (I had that first) stiffened up the back of the car. but with all the changes I made over the winter (including the rest of the trunk cage) who knows what did what.
To answer your question directly.... the only real answer is: "maybe."
I'm not huge on "cosmetic only" mods, but the trunk cage is some serious "pimp points" regardless of real benefit in my book.