There are many sections that may seem complete, but need thorough cleaning. Final Fantasy 6 has most things ripped, but is missing paletts, tiles, and the organization is too messy. Additionally, I'm sure maps are missing good chunks and animated tiles. Trials of Mana is similar in that regard as well as A Link to the Past. These are just a few examples and I'm sure you can settle on something.
EDIT: Come to think of it, Alcahest has some really cool bosses that could use ripping. I don't know if that would be something you might want to do or not, though.
EDIT: Come to think of it, Alcahest has some really cool bosses that could use ripping. I don't know if that would be something you might want to do or not, though.