if ur wanting things like power spheres and the like, try using ur "extract . . ." abilities. if u use one on kodos in the monster arena, he will drop 40 after the battle (at least i think it's kodos, it's been a while )

first i'd recommend sending ur 3 main characters round the entire sphere grid. valley of the cactuars with triple AP weapons is good for this. you can also try zanarkand dome and omega ruins if u want some variation. of coure the don tonberry trick works a treat

to max stats after gonig round all the sphere grid, u need to kill the specie creations in monster arena. these will drop spheres to fill in the empty nodes to +4 of a specific attribute (unless ofc it's health or mana).

there's an exception to this. if you want to max ur luck stat, you will have to kill earth eater and the large watery sphere (forgot his name! ) in the original creations. earth eater will drop fortune spheres while the sphere will drop luck spheres.