There is no way to answer that - we have limited money/people/time. Whatever we fund - we will get whatever the returns are - but there is no way to know what we don't have because we didn't fund some other thing. Even if in a few years we fund that other thing - what we get out of those funds is influenced by the other things we already know and so whatever we get out of it also shows the results of the other research that we already have.

The only exception is if some research reveals nothing. Though this isn't a useful claim: "it doesn't work" still revealed something.