The bottom line is: Go see these places now, it will be even more crowded in say 10 to 15 years.
I was lucky that I enjoyed sight-seeing in my early years and that when I visited some of these places, I was practically alone or only see members of my own group!
As usual, Asian based airlines took up the majority of "providers" plus a few middle-east based airlines.
You can forget about North American based airlines, with grand-mothers serving you, you get nothing but nightmares!
I always feel taking a long ocean cruise is like a house arrest -- good food and nothing else to do. A river cruise, e.g. Rhine River Cruise, should be much more enjoyable.