Actually Aerith's house is in Sector 5, you have to access it through the Sector 5 Slums which just also happens to be the road needed to get to Sector 6.

Now I do get that what we're going to see with the remake is a larger expansion of these areas, I was simply pointing out that technically players have seen almost half of Midgar proper anyway in the original. As for seeing the top side, I feel that really comes down to a question of why? Obviously players are curious and wish to see it, but plot-wise, it makes more sense that AVALANCHE would steer clear of the top side of Midgar since it's got heavier control by Shin-Ra. Resistance movements usually don't like to stay in plain sight. Judging by what we see of Sector 1, it's likely a n industrial manufacturing zone. Sector 8 is an entertainment district, and Sector 7 looked like a housing district, which I imagine a lot of places above are, since I imagine the commerce section would be in Sector 0 with Shin-Ra hq. So I don't really imagine anything above ground would be important or interesting enough to really explore unless they become sidequest hell zones.

If you want an educated idea of what the top part is like, it's probably best to look into the original concept for Walt Disney's EPCOT project as it apparently served as part of the inspiration for Midgar. Especially noticeable as the whole concept was basically a studio town where everyone worked for Disney that lived in the city which is what Midgar is ultimately.