I know that aesthetically that the "plaza" looks COOL. What would be the in-universe explanation for this "plaza"? I am not being facetious here; I am attempting to understand this ship.
If power to the whole ship were lost (similar to TNG - Disaster
) it would give you the ability to access all decks on the saucer. I'm guessing there's probably some sort of ladder or emergency slide/chute access in the sides somewhere.
It might also be the central atrium around which the main computer core is wrapped, with entrances to the computer core access rooms along the rim.