Lets talk about Salvia divinorum. Salvia divinorum is the scientific name for a plant native to Mexico. The plant is closely related to sage, basil and other garden variety salvias. It is used by Mazatec shamen to induce visions and divine the future (thus the name "divinorum"). The scientific name literally means "diviners' sage".... "Sage" being not just the name of a certain family of plants, but also a word to describe a person who can see into the future, I find the scientific name to be intriguing, to say the least.
I did have a plant years ago but it died before I had a chance to grow it large enough to harvest anything off. Sorry I can't be more help there but what you say about the right way or frame of mind makes perfect sense.
It is the same with Ayahuasca and most western spiritual seekers are expecting a psychadelic 'trip' to 'woo-woo' land but often end up with throwing up, sleeping for 10 hours and feeling like crap the next day.
Dreams are similar, our frame of mind and subsconscious rattlings are supremely important in what type of dream we have.
The Mazatec consider Salvia to be a holy sacrament, hence all of its names in some way reference spiritual divination and the Virgin Mary. When a curandero sets out to gather the leaves of this sacred plant they will take extra precaution not to accidentally step on any of the surrounding plants, they will kneel down and offer a prayer to the plant before and after they harvest its leaves. After the leaves have been used, the curandero will go out of their way to discard the plant remains in a secure place, where it will not be trampled on by other people or be disturbed by foraging animals.
For centuries the Mazateca Indians have used Ska Maria Pastora in their ceremonies to diagnose illnesses, aid in healing, see into the future, find lost objects and to identify robbers. If a precious object was lost in the forest, the Mazatec Indians would call on a curandero to perform a sacred ritual. The curandero waits until dusk, places the person who lost the object in a very dark, quite place and offers a prayer to the plant. A potion is then made from the leaves and administered to the person; while the person is experiencing the effects of the potion the curandero carefully listens to everything the person has to say. The following morning the curandero uses that information to help them find their lost object.
From this site (http://www.entheology.org/edoto/anmviewer.asp?a=83)
So it isn't the Curandero or Curandera who is consuming the herb - that is interesting in itself.