I usually don't put too much energy in any "fourth character", especially not Minh and Josef, since they leave pretty quickly.
I usually just throw on them any remaining equipment and let them handle the whole thing as well as they can.
I tend to get Josef a Cure and Fire spell though, but that's about it.

The only character I could say I *really* care for would probably be Gordon.
Yes, he sucks badly in the beginning, and that's exactly why I train him a lot, cuz he's supposed to join me in the Warship, the hardest damn part during the first five hours of the game.
I boost his HP forever and bring him great equipment.
I even tend to visit Mysidia, just to get him the Flame Spear, and even then I'm having problems in the Warship. :rolleyes2