Not so much. Those with higher incomes and who have come from privilege tend to be less polite and won't think to say please and thank you as they kind of expect people to just do things for them and show them respect and they don't even see people like service workers as human beings. Poorer people have likely worked those kinds of jobs themselves so are more understanding - I've had cashiers apologise profusely over stuff that's entirely out of their control, and I always feel bad for temporarily making their job harder because I know what it's like. Saying that though a lot of poor people can be rude too and think that the world owes them everything. I grew up on a council estate and those places can be terrifying, and people are more likely to be violent or steal. So it's more about upbringing than wealth, entitlement can work both ways.
2. Can the idea of good manners inhibit people's natural sense of fun and inhibition?
No. Anxiety and good manners aren't the same thing - in fact it's usually more confident people who are happy to greet strangers and hold doors open and stuff. You can be considerate of those around you without ruining a good time, and having a good time whilst being inconsiderate makes you 100% That Asshole.
3. Do people have more manners now or in earlier times?
It's tempting to say people had better manners in the past as people are much more selfish and "me and mine" focused nowadays and don't seem to discipline their kids, but with wider class divides, racism, ableism, homophobia, and basically a far more judgemental attitude generally where it was really easy to become a social outcast - I don't think that's good manners either.
4. Do you say "hi" to people even if they are strangers? Why? Why not?
This is a huge country/city divide thing actually. I'm from London so I grew up not saying hello to strangers because there's so many at any given time, and it would waste people's time to stop them to say hello even if you do know them - when you live in a major city wasting peoples time or getting in their way is far more rude than ignoring them. I found it really jarring when I then moved to a small town and strangers I passed in the street would say hello - I'd spend time afterwards racking my brain to try and work out if I knew them because I didn't understand why else they'd talk to me. And although I know it's considered "friendly" I still don't say hello to strangers unless they say it first because to me, when I'm going for a walk I'm either alone and want to be left that way or I'm with someone and don't want to interrupt our conversation because some rando has butted in just to say hi. Some people can get really forceful about saying hello and will get really judgemental about your reaction, and I don't see how that's considered more polite then leaving people to their own business?
5. Do you listen to other people's conversations on the street?
Sometimes. Not in a deliberate nosy way, but in a passive kind of way. I like to sit in coffee shops and people watch, so I usually pick up snippets of people's conversations, but I'm usually tuning in and out of various people around me, I rarely focus on anyone in particular unless their drawing attention to themselves and making a drama. I think when you're in public you should expect other people might be able to hear you.