The Effects of "Seeing It Live"

Having many favourite artists, I am always wary about seeing any of them perform live - I have been disappointed before and am not really willing to spend money on a concert that will not live up to my standards.
I really enjoy the Transiberian Orchestra's Christmas arrangements, so I went to their concert at the Rose Garden (Portland, OR).  While the music was still the stuff I've been listening to for years, the concert was nit to my liking.  It was like a rock concert, but EVERYONE stayed in there seats.  Because of the conflicting performance energy to audience's relaxed seating, the concert lost enjoyment.  I would have liked the performance to match the relaxation of the audience
I've also been to concerts where I've wanted the opposite - I wanted to be dancing around and all with the performers...

The question is - how does the live performance change your view of the artist?
There have definitely been concerts I have attended that have caused me to re-evaluate my devotion and some that have strengthened it.  The Oak Ridge Boys are a group I rarely listen to outside of a concert - it was kinda a family tradition to see them in concert in Branson, MO when we went on vacation or in the Wisconsin Dells, WI for the Christmas concert.  I love going with my mom and sister and singing along!
The merchandise is important too - sometimes...I have bought CDs at concerts, but I've never got any t-shirts or posters or photos or anything else.  Is the concert merch important in one's following?

Have you ever seen someone(s) and had your view of them completely changed??  Have you ever purchased any merch at a concert that has affected your following of an artist?