rear sway bars will stablize the rear, but it will create more OVERsteer as opposed to UNDERsteer.
with over steer the car has a higher tendancy to spin out or have the rear end kick out. When your lose control in a turn your supposed to turn the steering wheel in the way th car is turning and gas it, so just just spin out. With more understeer you have a better chance at correcting the car when its losing control and all you have to do is stomp on the brake (which is most peoples reaction)
So just keep that in mind that if you put on a rear sway bar it will firm up the rear a lot but if you like tearing up windy roads and freeway on/off ramps your car will have a tendancy to spin out and do not try to correct the wheel (youll be all over the road and the outcome wont be pretty) just turn in and gas it so you do just spin out
Yeah, a rear swaybar is definitely worth it! Adds a bit more stiffness to the car and handling is slightly improved. Also, it is really easy to install and shouldnt be that expensive. (I paid a friend $40 for his off of his 00 GT)