iLife '07 is not guaranteed to be released in January but there's a good chance it will be.
i doubt there will be any improvements to the iMac since no new chipsets are expected for January.
if it doesn't hurt you to wait, i don't see why you should rush into anything right now.
Yes, iLife and iWork have always, since they were introduced, been updated in January, at the MacWorld Expo.
If you look at the frontpage, there are pland for a "Core 2 Quad" chip, which I think would be ideal for the iMac. And besides the Mac Pro, the iMac is the product next to the MacPro that has had the most time since an update. I think there may be a chance that Steve will announce an iMac at MW, which will ship in a month or so.
Just wait until MW. There is a slight chance Leopard will also be out by then.