History of science has consistently shown that when you push the boundaries not only do we find the things we were looking for, but lots we didn't realise existed.
The space race purpose was to get to the moon, the rest came as a by-product of that attempt.
I'm sure some will say that the money spent would be better off spent solving world hunger or cancer research. However this ignores that science is inextricably linked, and a discovery in one area could affect another.
The problem is, if we knew what we were going to find, there is no point looking for it. And once we found something, there may be many many ways to apply it. For example the original quantum research, was purely theoretical and many would of said pointless, yet know we are using the quantum realm in electroncs, computing and starting to look at biological processes in a new way
Biting the hand that feeds IT
