Margarita,
From my end of things I think a little goes a long ways. Just because Joni Mitchell and others are capable of multilevel octave acrobatics is not an excuse to do so. It has the same effect on me as some dental equipment. Singing with a vocal vibrato can be ver effective. I still love Buffy Ste. Marie fr'instance. It all depends on the song and the situation.
Oh God, protect me from Minnie Rpperton and "How Gentle is the Rain."
Don Meixner