That'* a little extreme to say you'll need to rewire your entire car. You won't. If you replace the factory head unit, you'll also need to replace the factory speakers, and you will need to run new speaker wires. None of this is difficult, stereo installation shops literally do it every day for a living, and you can do it yourself if you have some spare time.
Frankly, there'* nothing sacred about the factory Bose system, you can certainly do *much* better for sound. However, some things to consider are: The factory Bose system integrates with the heads-up display if you have it, so you'll lose the radio information display if you go aftermarket. Also, if you use GM'* built-in OnStar, it uses the factory radio and speakers for the output of OnStar communications. And finally, if you have steering-wheel controls for your stereo, you will lose that functionality unless you also install an adapter that converts the steering wheel controls into Infra-Red remote signals, -if your aftermarket head-unit supports a remote.
If you were going to lose steering wheel control functionality, I suppose another option would be to replace your steering wheel with one that didn't come with steering wheel controls, for a nice appearance without the disgrace of disfunctional steering wheel controls.
Personally, I wouldn't hesitate to rip out a Bose system.
97 SE, teflon wiper blades, Dunlop Sport A-2 tires, Leather steering wheel cover, Pioneer DEH-P480MP mp3 CDRW head unit, Pioneer 12-disc changer, iPod hookup, Boston Acoustic 3 way 6x9'*, Boston acoustic separates in door pods, Alpine 4 channel amp in trunk. Magnaflow dual outlet muffler and Ractive stainless tips. Autozone rice pipe and K&N 4750 intake kit. Clear corner lights. Energy Suspension end links.