The problem with this kind of argument is what I'd call the "Bozo the Clown" rejoinder:

It's true that people spent a lot of time investigating something that decades (centuries, millennia) later came to be seen as useful. But it's also true that people spent a lot of time investigating things that didn't.

From the perspective of the present when people are doing the investigating, a strange discovery that has no use can't easily be told apart from a strange discovery that has a use. All we can do in that present is judge the technology on its current merits - or try to advance the frontier. And the burden of proof is on those who try to advance it to show that it would be useful, because the default position (which holds for most discoveries) is that they're not going to have the kind of outsize impact centuries hence that number theory did.

Or in other words: It's a bad idea to assume that everybody who get laughed at is a Galileo or Columbus, when they're more likely to be a Bozo the Clown.