Would you allow the magic of Mystical Rituals?

Basically the shaman can perform rituals that have powerful effects, but the rituals A) just come to him somewhat randomly (based on the needs of the village and of the land) and may only be used once or twice before being forgotten, B) can not be forced, C) take time in addition to their other requirements. 

Example: Rain Dance

Starting as the last of the light leaves the summer sky the Shaman guides a circle of villagers (6 in this case) in a dance around the fire while each member is burning a different plant in their hands and a fire in the middle dances with them. Each villager that is part of the circle has been prepared a head of time with various paints mixed in various ways by the Shaman. As the villagers dance, clouds cover the sky and a light rain begins to fall. So long as the fire remains lit and the dancing continues so will the rain. Many circles around the fire and as the forest itself quiets the dance ends, both the shaman and all those who participated fall asleep where they stand, falling gently to the ground. When they wake they find that it rained just long enough for the village to get the water it needed for the next week or so, maybe a whole month.

Requirements for this dance:
6 Willing villagers - this is likely to be an act of desperation on their part considering the fear of magic.
7 Different herbal plants collected into bushels - can be difficult depending on the season
7 Different mixtures to paint on the shaman and villagers - Each mixture is likely to use different ingredients
A large Fire - Fairly easy
Time - About 6-7 hours in this case (9-10 at night to 3-4 in the morning)
Energy from all of the participants - each person who participated will feel as if they haven't eaten in a week or more, and will need nourishment soon.
The planets energy telling the Shaman what to do - GM hack in here. As GM you would decide what rituals are received, as well as the base requirements for it, by the Shaman while he meditates each day, if any. It is then up to the Shaman to use them.