It's not just the 12 kids. With the money spent Thailand is paying for a belief in the minds of its people: that the government would do the same for their kid.

I'd argue that this kind of belief is extremely valuable for a country's economics as a whole. In order for the populace to be economically productive (and save 50000 kids from dying of diarrheal diseas) you need to create a safe, reliable, and predictable environment. Governments insuring against events like kids getting lost in caves is the way that they get that.