You're not wrong there. Likes are one of the easiest things to obtain, as it's least effort for a user. I have tested a number of different promoted posts etc. and spent 19CHF on promoting a post for our new site, with URL and Image (increases visibility apparently) and monitored the traffic.
Although I had 1190 likes on the post, the total number of site visits was only 237.
Promoting posts can be good though, if you have a product especially. You can link it to a deal on your website shop etc. and this can drive customers to the site, which is where you want them as more chance to sell more.
We're in a bit of a weird place for making the most of this, I am merely trying to build up interest. We target educational institutes, so facebook as a direct marketing for sales wouldn't really do that, but if it helps with branding (when I do business development they might have seen our stuff online, or check us online post meeting and a strong following reinforces we aren't a made up entity etc.) then that will be worth it.