score:5
I was actually very curious that you were considering 'sandals' for hiking - a brave man. Until I clicked and realised there was such a thing as Hiking Sandals.
Anyway, I did some research and found an article about when and why hiking sandals can be a bad idea. The credibility seems pretty sound - he actually recommends the Keen range (even has some affiliate links to them), and explains when they have issues.
I think your biggest problem could be sand getting in and causing rubbing. In the cities, you'll likely be fine if you're not carrying a pack too much - I wore closed shoes and socks in ultra-hot, dry climates last year and didn't have much problem - as it's dry the feet don't tend to sweat as much as they would in say, Singapore, where it's humid and hot!