Ghostlight raises a great point. Think about your own job? In what ways is it repetitive, challenging and think how often the staff challenges and are things happen in the work place that either boost or lower morale. I'm sure working on a show has similarities.
At the end of the day what makes or breaks a workplace is the people. There are days I don't like my job but some of my co-workers make it bearable. Then there's the vice versa-the days where I find my job inspiring. I'm sure its similar for actors. They do what they need to do and probably rely on friends in the cast to keep fresh.
I agree with the ghostlight that audiences most likely do impact actors since it is an energy exchange. I had a friend who went into WIcked and he loved always having a responsive full house and hearing people go nuts on "Defying Gravity." He said it is the best thing in the world to see full, responsive audiences.
On the other hand, one of my friends was a local wig master for a touring house and she said some casts, like the one for Titanic were pretty run down and sad after months on the road with bad reviews and less than enthusiastic audiences.
"The sexual energy between the mother and son really concerns me!"-random woman behind me at Next to Normal
"I want to meet him after and bang him!"-random woman who exposed her breasts at Rock of Ages, referring to James Carpinello