First, even if you change the seats you won't gain that much. Unless you go to racing seats. That's going to be a lot of fun getting in and out of on a daily basis. Not to mention that they are designed to be fastened to other things like roll bars for proper securing. Other aftermarket seats may be more comfortable and give you better side support than stock, but weight savings won't be one of the benefits. You might save 20 lbs, maybe, and on a car which weighs as much as a G that's a drop in the bucket. The main weight savings if you go that route will be in your wallet.