You definitely don't need an expensive "workstation" card, especially if you're just starting out. Complex scenes would get a little slow in the viewports but we're talking huge scenes that a beginner probably wouldn't encounter. I've been doing fine with a 9700 Pro - Silo will go up to around 60,000 faces before it becomes unacceptably slow, can't remember where 3DS Max starts chugging.
Even so, every package/modeler that I know of (especially high-end ones like Maya/XSI) feature layers, or at the very least object hiding, either of which would significantly improve viewport responsiveness.
So unless you see yourself working with big, geometry-heavy scenes from the get-go, save yourself some money. I don't know what card you have now but something like a 7600GT may even be overkill ... but it never hurts to have a little more oomph.
Edit: Money is better spent on a fast CPU and a lot of RAM (doesn't have to be fast or low latency). GPU is only used for viewport display, CPU does the rendering unless you're using modo which, as far as I know, is the only package that employs the GPU for rendering.