My personal opinion is keep it to a 30 second ad. Don't go the 60 second spot. You loss them. 15 second spots are hard to come by but were very effective for our haunt.
Also we have done two different promos onsite even offering it as a sign up for a chance on a cruise, didn't work out anything like I thought it would. Could just be our area but we tried it for our Hallween store as well and offered a 20% off entire purchase, didn't seem to work either.
We found that radio wasn't as good as grass root advertising, monsters on the streets, parades, at a large function promoting such as a fair, etc. Oh and we got a lot off of billboards and the yard signs along the highway.