KH1- I remember running around all planets worlds earning 3 experience levels each world. I did this before the end battles/Ansem.
KH2- Presently i'm beating the game for the 3rd time on Proud and I've yet to go back to Hallow Bastion before you fight the guy with the Sitar... That battle is coming up soon but what i've noticed is that before any big boss/organization fights there are enemies that give high experience points when defeated, for example: The Curly Hill in Halloween Town, Also the Area where you meet the organization for 1st time at hallow bastion- I think the area is the Basin or sumthing... where you run into the Final Fantasy 10 little treasure hunting trio chicks.... When my drives are full i go to an area that has many enemies and when i'm surrounded... BUST OUT WITH THE ROXAS MODE!!! It's been working well for me, each time i defeated all the enemies on that map, i hit the gummy ship then land on that same planet again- It will reload all your enemies automatically. Sounds like a long time to level up? Not really- Remember the stronger you become the more easier it is to defeat the heartless & nobodies... I hope this helped sum!
ps- when is Final Mix coming to USA????