There isn't a Lazer ZXR/S. It's definitely a Lazer ZX or ZX-R, the ZX-S is quite a different beast. A picture would identify exactly which version it is.
Good cars, they are perfect to get you going and more than capable at club level. The nylon front gearbox solves the real achilles heel of the car, the other is the wishbone mounts which I suspect will have been replaced with alloy mounts already. It will handle any modern motor you throw at it.
Most of the spares are still available to order from Time Tunnel Models and Ben racing.
Modern high end buggies do have some advantages, such as much more adjustability, but most of these advantages will make no difference to you until your driving improves. They are good solid cars that can take a beating, a modern 4wd will be lighter but won't take the beating of a beginner like the ZX-R. Once you get the hang of racing you will then have a better idea what you want to upgrade to.
Bodies for the Lazer ZX-R aren't available. For bodies Kamtec do the Optima Mid Custom body which can be made to fit, for the ZX body see here
http://www.tamiyaclub.com/trades_model.asp?cid=48650