Ticketed events aren't the only way to go though. I.e the upcoming Harry Potter Social Meet up which will probably boost attendance as well as gets an increase in merch sales. Tie event related festivals to the Convention center schedule. Nintendo World Championship is being held at the convention center, throw a free Nintendo event in the park. PotterCon is coming to town, throw a Potter related event in the park for all guests.
Money is made by having an interesting concepts. I.e TDL and USJ both sell waterguns in the parks for Water Festivals where they put on shows and parades that involve interaction with the guests and the actors and guests both get drenched. Mardi Gras at UOR and Summer Night EDM Festival are no extra charge despite Universal having to pay for the musical guests who come and perform however the parks get packed and they make money otherways.
HHN has an upcharge costs because of the increased staffing, paying the outside IP owners, and hiring certain special acts cost a bit for the length they do it.