What if you guys did like a special GM hunt? You could get players to pick up a free event ticket (guest or participant) from some npc or such, maybe make a small town map with good hiding places, like accessable rooftops, alleys, stalls, crowds of useless npcs, ect. Players teleport to the center of the city, guests to some floating viewing station or stands. The countdown begins and off they go! The event managing GM shouts out across the map either "Find the GM doing/wearing/holding [...]" or "Find the NPC doing/wearing/holding [...]". First person to say "1-2-3 on [...]" to the GM or clicks on the correct NPC wins that round, and 5 points, everyone goes back to the center and the next round begins. You could do this for several rounds, and then give out prizes to the top players. Every participant could get like 10% of their exp bar filled, so that it doesnt encourage only low levels to participate. Top prize could be some sorta event/cash shop item, next down some cash shop diamonds, ect. The guests can enjoy watching a lively sport, and have access to event only cash shop items like a sports shirt/hat/foam finger and non-cash shop items like "Cotton candy" or such. That way even if your just watching its fun, and it will encourage people who are watching to buy stuff from the cash shop.
Let me know how it sounds~