Removing back pressure can also make the car *safer* than stock as it is less det prone, the risk comes from if boost rises more than safe levels and is left unchecked
Do it once, do it right, big downpipe and no cat, then that box is ticked
If you buy a tactrix cable you can look for yourself at how it's running (you can look at if it's pulling ignition timing, etc), or you can chuck it on a dyno for a $150 power run which can a) listen for knock and b) check the state of the air / fuel ratios to put your mind at ease
The main thing is if in doubt just find out - remember it's a 15 year old car which hasn't had an easy life, it is as prudent a thing to do now and then as an oil change if you're planning on looking after the car