Problem with unofficial events is the prizes. Since you cant just spawn prizes, you have to use your own items. Not many people want to do that, nor do they have enough items to equal even 1% of the items given away during official events, such as Halloween or Christmas. This is why unofficial events usually have a poor turn out. The key is to find something that's fun even without prizes. Make something that people want to play for fun, not because of the prizes. Take my race event, zombie event, joy gun shootout event, etc. Sure the prizes were crap and most people said they didn't event want a prize, but damn was it fun for everyone who participated. That's really the best you can do as far as unofficial events.