Fixed. A lot of the sound systems Bose makes for foreign car companies are actually pretty decent for stock. For GM, however, it's just a name slapped on a practically unaltered system. For all the hassle you're going to go through, it will make next to no improvement in overall sound quality.
I'm with Confusingboat. I say sell the speakers and HU for whatever you can. Don't worry about the wiring. There's practically 0 market for converting to Bose since most people feel it's junk/not worth it. The buyer(s) will most likely be looking to replace a busted HU/speakers, so the wiring most likely won't be needed. Take the money you get, and put it towards some half way decent aftermarket speakers. If you shop around a bit, you can find a good deal on decent new speakers. Or keep a look out in the For Sale section here for good deals on decent used, good condition audio equipment.