1.The first sentence looks like it's some slang, or dialect, or just wrong construction - I can't really understand what it's supposed to mean. It looks like your guess, but it's so strange... 2.In Russian, when you want to say "to look at smth" you use preposition "НА": "Я посмотрел НА нее" - "I looked AT her". Here, author wants to say that there are places except Petra that are worth visiting and looking at them (meaning "enjoying the view"). Russians use the form "посмотреть НА ..." when they speak about famous places they want to visit. For example: "Я бы хотел поехать в Париж и посмотреть на Эйфелеву башню". 3.That sentence means that author visited a number of places today and he doesn't want to rush. Literally it translates like: "That's why I'll leave the ancient city for tomorrow - for dessert". He wants to take some time to rest and think about places he visited today, and leave the last place - the last bite, "the dessert", for tomorrow. 4.That construction: "Чего здесь только нет" means "there is no such thing in existence that can't be found here" and used, as you said, in situations when there is A LOT of things you talk about. But usually after such construction you start to list things instead of naming it by its common attribute. For example: "Чего здесь только нет: специи из Индии, Китая, из арабских стран; сладкие, острые, пряные, на любой вкус!"

It can be used other ways: Куда я только не ходил! Чего я только не видел! Чего он только не говорил! Etc.

We are joking about the phrase/idiom "чего там только нет!" ourselves:) Indeed it can be understood in two ways. It means "WHAT only they don't have there?" "What is that thing they don't have there?" A rethorical question: "it is hard to name such a thing". And then usually we list what they have. But it sounds so much like "what they don't have there? They don't have this, they don't have that..."