It might be a useful effect for small electronics in damp environments where solar isn't a great option. Caves, rainforests, showers.
In short it won't be. Less than $100 in a century during the highest recorded rainfall in the US.
Q. What if you strapped C4 to a boomerang? Could this be an effective weapon, or would it be as stupid as it sounds?
A. it's the second one. Aerodynamics aside, I’m curious what tactical advantage you’re expecting to gain by having the high explosive fly back at you if it misses the target.