As DDO has evolved, players have far more hitpoints now than they did earlier on and damage inflicted in various quests has ramped up dramatically, yet the Heal spell remains the most potent single-target healing spell a Cleric or FvS and, barring crits, it no longer even approaches enough healing capacity to keep a 700hp Barbarian healed.
To fill this "doughnut hole" in the healing line of spells, I would like to see a series of single-target and mass Healing Amplification spells introduced into the game. I'm thinking a single-target 10% amp level 4 spell, a single-target 20% amp level 6 and a single-target 40% healing amp level 8, with mass targets of 10% level 5 spell, 20% at level 7 and 30% at level 9 (though perhaps a percentage based on x+ caster level would be simpler).
So under best circumstances, we'd be talking about a 300 point single-target Heal increased to 420 points and a Mass Heal increasing from 300 to 390- hardly game-breaking amounts but they take a staple of high level quests and raids and make them at least a bit more effective in dealing with the damage output of newer content.
Problems:
I do understand that there is a fair amount of healing amp feats/enhancements and gear in the game, so provisions to deal with this existing capability would have to be made so that no one would be running around with an unbalancing 80% healing amplification. My initial thought would be to prevent spell and feat/enhancement/gear benefit to stack- a simple enough fix I would think.
Honestly, that is the only speedbump I can think of offhand, though I'm sure others can think of additional ones (and I hope they do so).
EDIT: second possible concern- do you apply the crit heal percentage, if successful, before or after the Heal Amplification spell effects? I would say after.