I don't recall ever saying I had mana problems, did I? No didn't think so.
So calm down and put your nerd rage helmet to one side.
Yes Divine Aegis is good, no-one is doubting that. But it only works on Crits, Improved Healing works on every Penance/Greater Heal and is a sizeable drop in mana cost. And yes before you say it, I know we get a lot of crits with Penance/Flash Heal etc. I'm simply trying to change somethings about to see what works best for me.