If it makes you feel any better KH2 FM was nowhere near as worth the buy as KH FM. The extras were nice, but they seemed lacking.
Kingdom Hearts: Final Mix2 new difficulties (1 easier then the original easiest difficulty, 1 harder then the hardest original difficulty)
1 new boss fight (Xemnas)
11 new Heartless
6 new weapons (2 for Sora, 2 for Donald, 2 for Goofy)
10 new abilities
A few new cutscenes
Gummi Ship Missions
and 3 new Ansem Reports.
Kingdom Hearts II: Final Mix1 new difficulty (Harder then the original hardest difficulty)
Cutscene viewer
New Heartless
7 new bosses (Vexen, Larxene, Marluxia, Lexaeus, Zexion, Roxas, and Terra)
2 new sidequests
New reaction commands
1 new Drive Form
New weapons (2 for Sora, unsure of others)
New accessories
New abilities
New synthesis items
An arena to refight all of the Orginization XIII members.
I dunno, if you ask me KHII has more new content.