The stock resonator is the worst restrictor in the entire system. I put a set of Magnaflow SS mufflers and had a custom Y-pipe made in SS. I like the sound of it. I'm looking at buying another SC and as soon as I started mine up the guy says "You did the exhaust, man that sounds nice". His SC has blown HG's at 100,000 miles and his exhaust is stock.
The stock exhaust is stainless steel and unless you really plan on some heavy modification to your car I wouldn't replace the entire thing. Just the mufflers, resonator and cats. You can put a Y-pipe on there for around $75 and if you don't like it you can put a resonator of some kind on there.
I have a 90 SC with 130,000 miles on it with a 10% pulley on it and I have no problems at all. I make a solid15 lbs. of boost at 5,000 rpms. with no detonation. I have a few other mods also but the pulley really picked up the performance. You will actually be able to feel the increase in power until you get used to it and then you will have to do something else to make it faster.
Just my .02 Bob