Don't forget a tripod. Traveling on your own you'll get opportunities I didn't. I brought one, but the cruise schedule(and the rain/fog) didn't give me a chance to do much setup. No control over duration at any given location, or time of day for photo ops. Should be different for you, so be sure to take one along.
The 17-55 should be fine for low-light shots, and be a great walk-around. I still don't see the 70-200 being very convenient. Its not wide enough and not long enough. But, everyone prefers different FL's, so better to bring it along than regret not having it. I wouldn't upgrade to the f/2.8. Even in the dreary weather we had, f/5.6 on my 100-400 was fast enough, and I rarely shot my 17-40 at f/4. If you have a burning desire to spend the money
, I'd consider a fast prime. Pick a length, 50, 85, 135... It would give you something different to use on people, flowers, wildlife....., being a bit more creative(shallow DOF) vs a zoom.
P.S. Its too early to think about next years vacation. Trust me, I did it for the last year, its best to put it out of your mind for a while 