Fishing enhancers like Rada's Blessing and Spirit Flakes would be way more valuable to training vs resource gathering if they offered xp for the bonus fish caught. Even if it's not a 1:1 ratio for bonus fish to xp. The idea of this comes from the Mining Enhancers like Varrock Armor, Celestial Signet, Mining Gloves, and Mining Cape giving rolls at bonus ore that gives full bonus xp.
Spirit Flakes would more than likely need to be reworked into how they operate, possibly a toggle either Double fish or more xp something like that.