In terms of upgrades, Yoichi's Bow is the most impressive of the ultimate weapons. An incredible 34 more attack than the Ice Bow makes this a bow that might actually be worth using. It's also far more accurate than other bows, making it useful even for a mage (though it retains the 70 magic penalty, so don't forget to remove it when casting Spells!). As a nice side bonus, it casts Berserk 3 on the party when used as an item. You can find these by killing Black Knights in Castle Palamecia before you reach the Jade Passage, if you want.