The spells are truly well designed.
I was considering this idea; it seems to me that you prefer the use of "improved" sanctuary spells instead of class' special features, but i want to make my last offer anyway.
A battle, where probably a healer will be find, will last for one day. Historically - i mean- a battle started with few "rounds" of archery shots from the long distance, then the movement of the foot infantry and eventually the charge (to the sides or to the back of the enemy) of the cavalry. Fighting in armor with swords and maces were truly fatiguing, and after one hour (of course many battles lasted for longer, and many lasted even for shorter period of time) casualties and wounded were recovered from the battlefield. In the afternoon dead were buried, wounded were healed. The morning after, if there were enough survivors able to fight again, and if there were "reserves" the battle started again.
That is: a healer will use this spell once per day. So why don't grant him:
sanctuary 1 (1/day) at first level
sanctuary 2 (1/day) at fifth level
sanctuary 3 (1/day) at 10th level
sanctuary 4 (1/day) at 15th level.
...of course he can still memorize it whenever he wants, but those ones are given "for free" just because it is integral part of his job.
Steven McRownt