I'm one of those people that likes pushing the puck (the mouse) for most 3D stuff and Vector (bezier) work, but when doing textures or postwork in complementary 2D apps (PhotoShop/PSP/Painter/GIMP/etc.) the tablet is much more natural. Not to mention that with the tablet's drivers installed, the pressure sensitivity comes into play on most paint/drawing apps. And that can add an extra degree of expressiveness that a mouse could never achieve with the same software.

Of course you can use a pen as a mouse, but my feeling is that even though it may be more accurate, it's less precise. (Or is that the other way around?) Depending on your mouse rate, it seems there's more "fudge" room for dragging objects around. (But that same aspect makes drawing with a mouse seem more tedious. As where points on the tablet correlate to points on the screen, which makes much more sense for drawing/painting.)

I just know out of convienience, I keep both devices plugged in. When it's time to draw or touch something up, it's more than convienient to have the tablet ready to go.

I also figure in instances where surface or displacement painting can be done, a tablet would be useful for 3D work. Knowing how I do things, I'd use the mouse to manipulate the object/basemesh and then hop on the tablet to paint or sculpt.

Oh, and if you want to generate some randomness either when drawing or modeling - using both at the exact same time can produce some interesting side effects.

I'd say to keep the tablet and give yourself some time to get used to it, if it's not used much in the course of a year - then sell it. (What you're likely to get re-selling it shouldn't be too terrible considering the typical prices demanded on new and refurbed units.)

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
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There might be something worth downloading.