My "proof" that rear braces have an effect is more anecdotal than sensory. When I first bought my car, the rear window seal would creak when I drove over really uneven surfaces, like driveways and such. It lasted a few weeks before the seal settled. Then, when I added my RSB and stiffer springs, it came back worse than before. However, adding the rear strut brace completely eliminated it.

Also, I forgot to mention strut tops- even with a strut brace, the factory strut tops allow quite a bit of flex. You should do those before a strut brace as well.

 

Probably not too much since I still have stock rear strut tops. But in a few weeks when I add rear STi tops, it will be making more difference in keeping my rear alignment from changing under high loads.

 

Yeah, alignments are always worthwhile if you haven't had one recently. But if you plan to install new parts...