How much luggage will you be carrying? The more weight you're carrying, the more you'll want more gearing options, better brakes in the wet, and (what you didn't ask about) chuffier wheels. Which really adds up to a new bike if you're planning to ride self-contained.

If you'll be riding fully supported, then you could possibly get away with just a rear drivetrain swap. I'm pretty sure (but not positive) that with an '07, you'd need a mountain derailleur to accommodate anything bigger than 28T in the back. And if you stick with rim brakes, make sure you get pads that will stand up to mountain descents.