Given that the site is meant to be helpful for people to get information about Drogheda and services and general living in the area issues, I don’t think blocking the forum is a good idea. Most of the chathere is the sort of thing people are looking information on, so you will want it indexed by search engines and available for people to read as it will draw them to the site. If people are discussing things they don’t want the general public to read, they probably shouldn’t be discussing them on a chat board! 8)
So my vote is to keep the board public, it’s what you need to draw people to the site. Even if they don’t register or post, they will still see the ads and the information and likely explore further into the site. If they have to register, you’ll lose site traffic.