I'm all for upgrades, but what benefits would one see of this?

Most users would see no benefits at all, you are correct.

Users who want to run many third-party apps on the player simultaneously would be able to do so more easily. I think that's the biggest advantage at the moment.

Theoretically, users who have ginormous collections would get the benefit of more space for the database and cache. But If I recall correctly, the current player app doesn't take advantage of the extra RAM so not even this is a benefit yet (someone correct me if I'm wrong).

I think that theoretically the disk builder image would have less trouble when formatting large drives, but if I understand correctly it would need to be recompiled to take advantage of the new RAM anyway, at which point they could just fix its bugs so it works for the regular-RAM people too.