You can argue technique all day long, who has more training or more experience or even a wider range, but it all comes down to whether the performance moves you or not. Vanessa may not be the best singer of all time(I think it's Ella Fitzgerald, actually), but she is amazingly consistent, having seen her live many times. The sound of her voice stirs something in me, and has since day one.
Over-use of vibrato can create pitch problems versus the rest of a track.
For what it's worth, I once did a vocal on a track and at one point I managed to sing with vibrato. And you know what? My voice sucks, so vibrato itself doesn't mean anything. Ever hear Maroon 5's "She Will Be Loved" where all of Adam's vibrato is autotuned out? Friggin' creepy. Point is, vibrato has its place but it isn't everything.
Dan/NS