Dave, I upgraded from my trusty D90 to the D7000 last summer, I found the change really very easy indeed. Most of the controls and menus are exactly the same making the 'bedding-in' process really not too much of an issue so perhaps you can wait for a couple of months to see what happens with regards any new announcements. Personally, I'd go for the new D7000 now as there's not much cost difference over a refurbished one and you've got time to get any problems sorted out well before you go.
I'm off to Iceland myself in two weeks time (obviously it'll be a totally different experience weather-wise than yours) but I'm definately packing my D90 as back-up. With all that water and rocky surfaces there's a distinct possibility of 'user error'.