"Increase stats by x|x if max hp" I would scrap ideas like this since rarely do you find players at full hp, and even if they are, it is a telling sign that the game is already won, so a small win-more is unneeded.
"Increase instances of healing by X" This is an interesting concept and pretty cool, but it brings 2 major problems. Miracle was made to not give EM, this would make it give EM, something not intended. The second is that with stacking, it would be too powerful (Increasing all sanctuaries' effectiveness by 25%? Holy!)