It's definitely true -- YA is has distinct idiosyncrasies and challenges in terms of PR, marketing, and directly selling it.
In addition, we'd like to thank everyone for their contributions to this thread. What is clear is that FB is not an easy social media game to play and exactly how to play it seems to be varied and nuanced.
In terms of whether or not Facebook has promotional value, what is incredibly interesting is that we just reviewed our very first FB posts made a few weeks ago -- before we had any people "liking" our author page.
Those first posts all garnered approximately "50 people reached" and various different levels of click-throughs likes and shares. That bolsters our suspicion that you can actually make posts on your author page without having any likes and mobile users are still being served up your posts if the posts are relevant to them.
Is there value to that? Yes, we think so... especially since you can make your posts on your author page into mini-floating banner ads (with different photos that include the title and link to your Amazon page, and catchy quotes from your book, etc. and use hashtags and connect them to your Twitter feed and Good reads page) AND especially if they are being seen by a different pool of rotating people each day and NOT just your "likers". And especially since you can pre-schedule the posts to run on different days, and then never think about it again after that for weeks.
If it's an automated advertisement that's completely free, and you're reaching enough people, then definitely there's value there.