As a native speaker, I have to say that I would never use the second sentence, "Did you see what they had done to our city?", except to describe a state of the city that has passed. For instance, if someone had painted a wall, I would ask a friend, "Did you see what they have done to our wall?". If that paint was then washed off, the question would be "Did you see what they had done to our wall?" as that state of "painted" has passed.
As for the difference between sentences three and four, I do not see any. It's just as correct to say "Did you see what they have done to our city?" as it is to say "Have you seen what they have done to our city?". However, I would say that if you asked somebody returning from the city, you would say sentence three rather than sentence four, as "Did you see" implies that they could have seen as opposed to "Have you seen" which implies that they may not have had the chance yet.
For instance, if somebody went to a cinema the same day that a new film was showing, I'd ask "Did you see that film?". If we were talking about the film, and I didn't know that they'd been to a cinema, I'd ask "Have you seen that film?".
As for the fifth sentence, you're absolutely on point.
"Why else" is a common construction in conversational English, meaning, "for what other reason". Read that sentence as "For what other reason would they have a wet bar?" This is a rhetorical question, i.e. a question that has only one possible answer, used to prove a point. There is a wet bar in the limo, so if it's not to provide drinks, what other purpose could it have? One could say this is rhetorical use of Occam's razor; Mandy uses it in a cutting manner.
Best Answer
"Seeing one film" does not seem to hold a routine/habitual meaning so it does sound a wee bit strange.
For events that are more habitual in nature, then we often use "Do you ever ...?".
Do you ever go to the movies?
Do you ever ski at Aspen?
Do you ever snowboard/waterski/etc?
The meaning for "have you ever ..." is "have you had such and such a life experience" and for "do you ever ...", the meaning is, "is this part of the routine in your life?"
Sam: Did you ever see this film? Pat: Yeah. Sam: When was that?
Perfect tenses refer to the act. The action is important. Below is a dialogue between two friends who are picking out a DVD at the video store.
Sam: Have you ever seen this film? Pat: Yeah. Sam: Was it good?
Note that, for some speakers there isn't a difference between "Did you" and "Have you". They use them interchangeably. For example,
Ex: Have you eaten? Ex: Did you eat?
To me, however, "Have you eaten?" means, I want to know if you ate, and not when you ate. And "Did you eat?" means, I want to know when you ate:
Hope that helps.