On how to select what to fund in the future: find the brightest minds, fund whatever they want to do. That tends to work out in aggregate
It would have been worth what? Doing mathematical research at all? Nobody is suggesting we shut down mathematical research.
It doesn't justify a funding system that didn't exist / didn't fund those researchers. We need to come up with better reasons to fund such a thing.
Do we?
For most of us, it seems like the EV (expected value) from such funding is quite positive. The work pays for itself in the long run. That's justification enough.
But I would suggest replacing "seems" with the best numbers available.
I know there's research on it for applied and basic science in general, and the rewards were massively EV+. But I can't recall whether similar research covers applied and basic mathematics research.