I've tried FB boosting/Ads a few times for events locally. In summary, we saw no return on the effort. And I do mean effort, as it is a relative chore to set up the "boost" campaign (target audience, customized graphics and copy, etc.) - at least the first time around.
In my opinion, they have a pretty good scheme going - for FB. Their initial estimated exposure never materialized with the actual campaign yet the funds disappeared just the same. Their reports demonstrating "success" (views/placements) I found to be very vague. Over a span of three "campaigns", the only related post "likes" we got were from people well outside our targeted audience and geography (e.g.: people in India don't fit within 50 miles of Concord, MA). Follow up with new faces at the events found no one sourced from the FB ads.
We got better results from the local free toss-away "Action Unlimited" weekly rag, via their free community events articles. I've found Craigslist event listings have also worked - again for free.