I love the sectors and the whole atmosphere of Midgar.
There are some clues about life on the plate in OTWTAS: Episode Denzel, in which Denzel's father has been promoted and is moving the family to a new house, going from Sector Seven to Sector Five. In Advent Children Complete there's a sign in the rubble of Sector Seven that says "Shin-Ra Electric Power Company Company House", so I tend to assume that at least Sectors Five, Six, and Seven were residential areas, with a lot of ShinRa housing. Perhaps the sectors get more exclusive the lower the number, so Sector One is an aspirational address for company employees? Or maybe each sector has a mix of housing, schools, hospitals etc. and Denzel's dad just happened to like Sector Five?
Sector Eight seems to contain a lot of shops, bars and theatres. and in Before Crisis Rude arranges to meet Chelsea at a park - The Western Park - which seems to be in Sector Eight to watch a tree-lighting ceremony, so there must be some open spaces on the plate, although how green they are given the low light levels is debatable. There does seem to be a lot of housing in Eight in BC.
I think the player could have seen more of Midgar, but we also have to be mindful of not showing too much of Midgar. Players have the expectation of wanting to see everything, but a good worldbuilder knows that the key to making something, especially a massive city really seem massive, is making at least a good part of it unexplored to the eyes of the player.
Now what they could have done, was had the narrative or NPCs mention the other sectors more to make it seem more alive. "I'm in Wall Market all the way from Sector 2 to buy the dresses made here" or "I heard Sector 3 is really fucked up and dangerous, even moreso than Sector 1" or something like that.
I couldn't agree more. I love having so much room to invent and imagine, so I wouldn't want too much detail, but some of those comments you suggest would have been great. In my headcanon the Sector Two slums are very rough, and each slum sector, with the possible exception of Five, has at least one or two gang bosses who control things with ShinRa tolerance, if not overt support.
One thing I'd love to know is what the names of those original villages were. Do they survive, whispered subversively in some areas of the slums? I also like to think that there would be sporting and other kinds of rivalry between different sectors. Maybe each sector has its own football team?
In a fic once I called Reno's favourite band 'Sector 9'.