How low the level does the bonus give you enough xp that actually matters? The last time I checked it was like 15xp (not 15k) on a level 30s toon.
No, the quest says only 15xp, but the purple text after you kill it is much higher than that(on my lvl50 I was getting 15k from bonuses).
Honestly though, I don't mind too much if someone messes up and skips the bonus. I tell them nicely that they could have gotten more exp from the bonus, so that in the future they know why their team is yelling at them
Though, I did run into a girl with my guildies who was trying to free the prisoners while we were killing the elite O_O still think she was a troll, or just completely clueless on how the game works(she was messing up everything we were doing, but got kicked before the boss).
Back to topic, I have only been here for a month, and my first few KDY runs I was skipping every bonus because I had no idea they were there, it wasn't until this weekend that I found out about them
But now I try to make sure everyone I am running KDY with knows that we are going to kill the elite.