tail lights are a little heavy. just use a old set and remove the front lens. Tape the lights to the back side and throw a small amount of make a gasket to keep it to the car.
you can find at least 50-60lbs of BS behind the dash. all you need to do is fab few small mounts to keep it from falling off.
Ditch the stereo and speakers, drive around with an ipod and set of small desk top speakers if you need somthing to listen to. Use the space in the dash to mount switchs or your ipod. Factory amp is also a pound or two
Ditch the POS metal gas tank for a plastic one or a fuel cell
run coilovers in the rear(18lbs lighter then stock)
Fab up a new seat mount for the passenger like your drivers seat.
scuff the wheel wells for any excess rubber
Some of the GP rearview mirrors are lighter then others. If you have any lights or onstar on your mirror, find a basemodel one...or you can use some fishing line and your wifes compact
.
debadge it and use stickers.
the cheap aftermarket front bumpers weigh less then OEM..about a pound and a half or so.
The sunroof is heavy. I would not suggest replacing with lexan if you want to still use it. It would be hard to seal and might bend while going back in. The stock one does slightly but its thick and can take the abuse
It would cost about $40-50 in lexan to fab the tiny windows.....tho they are very light from the factory.