The stock bar on Neons without a rear bar is 20mm, Eibachs set is 24mm in front and 21mm in the rear. Suspension Techniques also has a set of sway bars that are the same size as Eibach for less, but without the bushings. Strut tower bars on the Neon are next to useless on the front. Even more importantly, the top of the strut towers is not where the Neon suspension geometry needs help, which makes strut tower bars useless as well. Now, strut tower bars on the REAR can be useful.
Neons can definitely benefit from more stiffness in the rear.
Be careful if you have a DOHC, some bars will only fit SOHC engine compartments. Springs Eibach makes two different spring kits that are stiffer and lower for around. Eibach also offers a Sportline set of springs for the Neon, they are supposed to be not as stiff as the Pro Kit series. Mopar Performance has released three different packages of springs. Mid, High, and Extra-High rate springs.