Definitely get the Steeda Subframe Bushing Inserts. Immediately. No question, just do it.
If you're not launching it, skip the brace for now; you have the 4-bolt rear and that is plenty strong. The resident ExST Street Racer Tyler Clark survived 65K miles and countless E50-fueled launches without a diff brace. Wait for JXB Performance to release their Diff Bushing Inserts, these will be the best option for you.