But the FF 10 International's extra features consisted of the absurdly hard Dark Aeons, and the even more absurdly hard Penance if you somehow managed to beat them. And by absurdly hard I mean 999999999999 damage per hit (that's not a joke). I think I killed 2 of them by being very, very lucky with Yojimbo, but that was after at least 100 tries. The fact they're there is really annoying, as certain locations can only be visited again when you've beat them. So you're not really missing much.
But I wouldn't be getting it for the extra optional bosses (heck, I didn't do most of the optional stuff in the regular version), I would be getting it because I think it would be fun to replay the game with the new Sphere Grid (not as linear as the one in the original version). I wouldn't pay full price for it, but if I find a copy in the $20-$30 range I'd like to pick it up.