Improving the graphics is sufficient.
Why would Square settle for sufficient, though? There's an opportunity, a budget, a desire from the company, and guaranteed sales to take a modern approach to this game from a storytelling, world-building, and lore standpoint. More depth everywhere. More to explore, more to see, more to acquire, more to learn. More.
They're not going to remake FF7 twice.
Square is going to shoot for the fucking moon with this opportunity to blow out FF7, and if they don't make it there, they land on a Cloud. And we'll all be supremely happy for it.