buy it now, what is there for them to update it to anyway, I don't think that it can get any smaller with current technology, capacity could be bumped up, but do you really need or want more than 1GB of music on a player without a screen?
Buy a refurb and save some money. An update may or may not come, but i see no reason to buy new when you can save a significant amount of money for the same exact thing.
Or, if you want the best of both worlds, the refurb store has 2GB Nanos for only $99!!!!!! (I know you want a Shuffle but for $20 more than a Shuffle new you get twice the storage, click wheel, and a color screen )