Do any superstitions have merit? Watch
Seen in this way, superstitious thinking is a misfiring of our attempts at pattern recognition. This means that the superstitious belief itself does not have merit, although it may by chance have positive unintended consequences. The practice of rain dancing might become a cultural tradition, which might cause villagers to bond, increasing social cooperation and make the village slightly more prosperous. Of course, there are just as many, if not more, examples of negative consequences, as would be seen with something very misguided like human sacrifice.
The mechanism behind superstitious behaviour does have merit however, since for example if you see someone touch a poisonous tree frog and die shortly after, you had better not go touching any tree frogs, and you'd help your friends and family by telling them likewise. Then 20 years later when someone accidentally touches one but doesn't die, you might've wasted some time avoiding frogs, but better that than taking chances.
Nowadays we have science to do frog testing though, so no excuses for us.