When you have a captive audience, even though they are captive, it's not forever; you still have to give them respect.
By that, I mean you have to give them some of what they have a right to expect (whatever that may be)—this'll largely be defined by the hype for your event but not entirely, and their expectations are important.
Word of mouth
You see, once they're no longer "captive" they'll be able to say what they like and if they felt preached to when they expected entertainment / whatever then that valuable commodity, word of mouth, will work agin you, not for you.
Pearls before swine...
If you cast pearls before swine, and all they want is feeding, fewer will come back next time. If you must cast pearls when they want feeding, cast some food they like, too.