Ah the age-old 'should I buy now or are updates right around the corner?' question.
I'm in exactly the same boat, the new nanos look pretty darned awesome and I'm considering getting one (today actually). But here's my view on the whole tech-upgrade thing.
If you want something, but you're scared it's gonna be upgraded soon, go buy it anyway. There are two reasons I see for doing this:
1) It is going to be upgraded, there's no argument there, whether it's tomorrow or a year from now, tech is just that evil.
If you buy it today, and it's upgraded next week, you can return it and get the new one. If it's upgraded past the 'point of no return' (pun intended), then sell yours on eBay, or to a second-hand apple store & get some cash back etc. Chances are though, that you won't care about the slight performance boost or capacity upgrade in the next version once you've got one. You'll be too busy enjoying it. (Case in point, I still own and love my 2G iPhone, I have no intention of buying a new one unless mine breaks or gets stolen.
2) Once the (inevitable) new upgrade comes out, you're just going to wonder when the next one will be. Just grab the current one and enjoy your gadget while ignoring the updates. In a few years, go buy the latest one when yours is totally outdated (unless you still like it, of course). Things keep moving, by then there'll be some crazy new features and you'll probably be ready to buy another.
Now, I'm off to Future Shop...