Well, if your going to do the scavenger hunt, you'll need to section it off for different levels (i.e., no Outland shots for those who can't get there, No Northrend shots for the few of us who haven't gotten WotLK yet, a lvl 30 isn't going to survive long enough to take a pic in the heart of Felwood, etc.) and it seems to break down from there.
Dodgeball would be cool, but only if we get an actual group together. Otherwise, we're just stuck with a bunch of balls (HA!)
Never been on a 'Raid' before...so I can't comment one way or another.
I'll vote for the mystery trip. Not sure of the details but it just sounds cool