what year is your stang? if its a 99+ dont touch anything unless you are running serious boost. its perfectly fine. ive seen 03/04 cobras running 600+rwhp on the stock ignition without problems. if you want swap out your plugs to some copper plugs.
I agree with previous posts about not needing to upgrade it. Ive seen on average 7-12hp increase from plasma booster. The only other thing I know of is the MSD Stacker 8. I believe its not much different from the plasma booster(correct me anyone if Im wrong) and its over $400. Neither one seems worth it to me.