It's one of those "once you do it, it's hard to go back" things. Priority boarding, roomy seats (or lie flat on many business international flights), free food and drinks (no food on short hops), etc. I find it worth it, if you can financially swing it.

Usually, yes. Coach or economy class really crams everyone in. In nicer classes you get more room, better perks, food, booze, etc. It's it worth the extra money? Depends. I got the upgrade once, it was a whole different experience, quite pleasant to fly.

Planes are miserable in coach on cheap airlines, it's pretty decent on nicer airlines like Emirates, Asna or Qatar.

Business you basically get a recliner sofa with lots of space for your legs a bigger screen and a restaurant level of meals.

For flights under 4 hours I don't personally see the bennefit, but the longer you're in the air the more worth it becomes. On international flights business class can be the difference between being crammed in for 12 hours and being able to lay down like a bed.

It is a significant upgrade but as someone who has taken numerous long cramped car trips I would not willingly pay for that level of comfort for a few hours.

It's okay, but it is no first class. She's still poor people, just not as poor.