Not really, this is just off the top of my head and I'm sufficiently unfamiliar with bot programming and FB advertising that I'm sure that plenty of better solutions must exist.

You are forgetting that there are growing numbers of programmers in developing nations for whom doing this sort of thing can be an attractive way to earn a living (or at least they are willing to try it). Look on any "hire a freelancer" type sites and you will find hundreds of postings for tasks that sound awfully like scamware development (usually at a couple of dollars an hour).

Browser hijacking is not so uncommon either, I've installed legit software in the past that has come bundled with some crapware that injects extra adverts into web-pages and other things.

The analysis would not be too difficult either, simply set a "click rate" and adjust it downwards until you are being charged > $0. Do facebook offer any method to get free trail credits? If so this could be abused, heavily.

The economics are roughly the same as with spam, if you do enough of it your "hit rate" doesn't matter so much.