I don't think there'd have been any way it would have been as pretty. Apart from the pre-rendered backgrounds and the FMVs, FFVII's graphics haven't aged gracefully. Granted, the pre-rendered backgrounds and FMVs would probably have been gorgeous, since FFVI has some of the best art direction in the series as it is. However, to me a lot of the charm of FFVI comes from the stunning sprite artwork. That would have been lost with polygons.

The music would likely have been even more awesome, as Uematsu would have had a more versatile synthesizer to work with. Dancing Mad with choral vocals like One-Winged Angel's? Yes please. (Granted, they already did that with Distant Worlds, didn't they?)