I've shot lots and lots of beautiful pictures (I mean - not only snapshots
) in a foreign country with just a camera and the DA 40mm XS.
It really, and I mean
really isn't about the lens...
That being said, I think you should bring
1. 18-135mm
2. (wide angle or 18-55 kit lens)
3. 55-300mm (for versatility) or a prime (for quality)
The beautiful thing of going there with your wife is that, if you find the time to go sightseeing together, the above setup can be used in a variety of ways, e.g.
camera A 18-135, camera B 18-55, 55-300 in bag (shared)
camera A 18-135, camera B 55mm prime, kit lens as a backup for camera B
camera A 18-135, camera B wide, 100mm prime for selected shots.
That makes a lot of sense IMHO, because you can cover almost all conceivable situations with only three lenses
and you can also swap them: one day you keep the 18-135, another you go artsy with the prime and the wide...