There's been a file in the FFXI database for over 5 years, it's called "Faith". Implement this spell for RDM only as a Divine Magic spell that's single-target and increases "Potency of Cure effect received +X%".
Make it cap at around 15-25% based on Divine Skill. This will give RDM the ability to have a stronger Cure IV. We really need stronger healing, as it's blatantly ridiculous that a Dragoon's "Healing Breath IV" heals players for 800-900+ for 0 MP and 0 hate but we've not had a stronger Cure spell implemented for RDM since 48 and only heals for ~580ish with good Cure Potency gear.

As an added bonus, give this spell to PLD as well.