Hi Kathleen
I am in animation since 1995, and I was used to work classically on paper, and that's the way I like it best. But the digital world evolved and in early 2000's I had to get a tablet, so I got Intuos 3 6"x8". I've used it for years, mostly for Flash animation and some Photoshop work, and didn't complain much, but then recently I've started working on a classical feature film done on TVPaint. So I did a little research and decided to invest into Cintiq 12", because I believed it would make me feel much more like working in the 90's on paper (I didn't go for the 21" Cintiq, as its too expensive for me and it also is difficult to carry around, although I'm sure that working on it is even a bigger pleasure). And I was not disappointed - working on Cintiq for me is the closest to analog way of working. But it's not true for all of my tasks: TVPaint is masterfully suited for Cintiq - the interface and all the functions are really convenient for Cintiq use, also keyboard use is minimum (which is amazing, cause my keyboard is behind the Cintiq and using it requires some effort). Drawing in some software like Photoshop is also easier with Cintiq. But when I need to work on something different, which involves extensive keyboard use, or precise clicks, or even worse - doing Flash animation, then it might become a pain. For example when I work on Flash, I use a regular tablet, cause Flash is a total failure on Cintiq and I need the keyboard a lot also. So in conclusion, I don't think I would have got the Cintiq if not for TVPaint.
Of course it's also a lot about how you are used to work, and in the end - what is the result you wanna get and the feeling you wanna feel and the software you intend to work with. Like Paul said, think well of your long term intentions. Cintiq is not a cheap investment and is not suited for everyone. I know people who learned to do wonders with a regular tablet and they wouldn't even look at Cintiq's. Coming from a regular tablet to Cintiq also requires quite some relearning and getting used to new ways of working, so your intentions need to be quite dedicated.
Personally, if you intend to work on TVPaint or draw a lot, I do recommend Cintiq over the tablet.
If you have the chance, try finding somebody with a Cintiq in your area, and play around with it...
Or well, you can always sell it - prices for used Cintiqs in good condition are so high, that you wouldn't loose much
P.S. I also like the paper feeling, so I use Wacom hard felt nibs with my Cintiq - feels like a soft pencil on paper.