Excellent question, there's a couple factors that must be first addressed to give you the most effective answer:

-Are the 75 participants loyal, returning guests or are they generally new faces?

-Do you offer upsells at this event? This opens the potential to reduce ticket door revenue to increase profit from back room sales?

-Do the events revolve around themes? This would allow you to generate consistent attendance and have guests bring friends to also implement this bi-weekly theme.