Insiders didn't get an advantage at all. All you had to be was a club member or a very active collector. After all, the event did really revolve around the club's membership, and rightly so. There was plenty of time except for they who were inactive for whatever reason.
When the "outsiders" started hearing about the tournament, there were, if I recall correctly, 30-40 spots left for the taking and those lasted about a week before they were gone. So....really, no excuse.
As far as having 400 entrants, I'm afraid that would just "cheapen" the tournament and the entrants would end up with a strike worth only $30-50. The entrance fee would have to be lowered below $100 also. I don't think many people would like to stay in Vegas 3 nights just for a $100 tournament.
Of course, all this is just my observation. Many people would love it just to interact with all the members.