I don't think we're ever in any danger of an all-paying calendar. As has been pointed out elsewhere, for some people running the event is the fun part, and paying the audience to come is almost a logical step if you look at it from the standpoint of "I want an audience and will pay people to get one".
That's similar to what I've said before: for quite a few events that I've seen, the audience are doing the organiser a greater favour by showing up than the organiser is doing them by having the event, especially for events that are empowering only to the organiser or hosts such as live music or DJing. People's goals in RL are not the same as those in SL, and just "going out to pass a boring evening" isn't something people will do in SL.