Here's the thing. Very rarely will it change the number of heals you need to cast to restore the party to health. Further, you shouldn't be casting that many heals yourself, out of combat healing should be done with wands, in combat healing is usually a wasted action, unless you have Heal, in which case the Healing Domain has some slight usefulness. Taking a domain just for it's effect on a 6th and a 9th level spell? Not a great idea.