I, too, am a hobbyist, but I've been adding to my collection of 3D apps pretty quickly (almost too quickly). I've purchased Poser 4 with PP, Bryce 5, ZBrush, Carrera 2.0 and Vue 4.1 with Mover 4, in that order.

I'd say that Vue 4.1 is a must purchase, but if you really want to do things on a budget and don't mind a steeper learning curve (and more limitations), you can get an OEM copy of Bryce 4 for $80 off the Internet.

Unless you want to model your own 3D objects, everything else is optional. If you want to do modeling, Carrera seems up to the task, plus it provides some tasty renders, but I do see some limitations to the interface.

I absolutely love ZBrush (it is my favorite app of all time), but I don't think you can count it as a true 3D program. It has some great features that allow you to do modeling in a very intuitive way, and to export those models, but it is not a full featured 3D app.