If you are going up for a public meeting, then Im guessing you are asking the city to do something outside of what would normally be allowed in that location. Those discrepancies would be the first thing to address. Either how is the impact of your use not really much different than a staff level approved use, or show how you are mitigating these new or different impacts. I'm guessing negative impacts to the neighborhood will be at the top of the list: parking, hours, noise, traffic, crowd control, undesirable out of towners, trash, police issues, etc. Add to that the basic operational safety stuff.
These people generally are not into the haunted house thing and have a stereotypical view of the industry and the people involved in it. Show them it’s a business and be professional. They are not interested in the visual elements in general except those that are visible to the non-paying public, such as signage and building painting. It is understandable that they don’t want an orange and black building with spiders after you and Halloween have come and gone.
While there may be statistics (though probably not) to justify some positive economic impact, as a start up operation, you don’t have much to offer. Focus on mitigating the negative and promoting the positive that is verifiable like community event and charity benefits.
PS im an architect with lots of experience with these groups and my better half is a city councilwoman and former head of the city planning commission, so I have some experience here.
Mid State Scare - San Luis Obispo and Santa Maria's favorite Haunted House
2013 - Hmmm, we shall see what gets conjured up