The only weapon I never bothered with is the one in the desert (forgot the name).
The underwater one is fairly easy once you figure out a good materia combination (I forgot it, but I remember that it was pretty bad ass). You need a crap load of materia though...
And I don't care much about my save games for RPGs once I've beaten the game, and left it there, untouched for months. That is, unless I level up every single character and do everything in the game... But I never do that.
