Hallow and wow - this is SUCH a great question and thread! Getting the word out is all well and good - BUT I am always concerned about out-of-the-area groups that come in droves -- then scope out things to prank, break or take.
We don't have a truly sophisticated haunt - one that charges or one that has many actor volunteers, etc. and so we cater to just our hood and a group of friends and co-workers to enjoy our set-up.
Still, our neighborhood has been "growing up." Each year - the little TOT's are older and now many are even in college from when we first started our home haunt in 2001. Fewer little ones means less traffic and then where are you with your haunt - "all dressed up and nowhere to go!" right? So we will be reconsidering this very question soon.
So if you do go hog wild on spreading the word -- know that your reputation will grow no matter what... With only flyers and word of mouth, our yard haunt grew to include a "FINAL BOO!" on Halloween night so that the neighbors and friends could come hang out for an extra hour. We serve hot dogs and cider, popcorn and pot luck. It would be costly and hard to manage, plus a shame to have it ruined by large groups from out of town.
Then there is the next big step that some home haunters CRAVE. TV coverage!! Right? But I offer a reality check - Unless you have the cohoonas to handle thousands, I recommend you hold off on that dream. Because we have connections with local TV media folk, we have been asked to allow film crews to come out and capture our yard decor. We always politely decline. There is the liability issue -- and then our neighbors would have a coronary if hundreds flocked into our neighborhood... bad drivers, boozers - -- the rude - the obnoxious - and then there is the public! LOL
So I guess my long-winded point is if you REALLY want to "advertise" your haunt, be sure to consider the ramifications of plastering your haunt all over hades ... Consider the range/reach for postings and how near and far you spread the invitation. Just how many people do/can you REALLY want to descend upon it!