I'm somewhat skeptical of the claim that researcher's level of interest in a given subject is very strongly correlated with the maximum possible benefit to society that could come out of an intensive study of the topic. It may be true, but I think that the primary motivation is just that the problem presents an interesting challenge.

That being said, I do think that scientists and researchers work harder and more efficiently when they enjoy what they're doing. If, as I suspect, interesting-ness is uncorrelated to potential benefits, we should still ensure that interesting projects are funded.

Imagine, in a hypothetical scenario, that there are two different areas of study that, if researched, would produce innovations of equal value to society. This fact, however, is not known to the individual running the research budget. Let's suppose (just for the sake of numbers) that a scientist who is actively curious about a problem will work 20% faster on that problem than an uninterested scientist. In this case, funding the interesting project will be more efficient than funding the uninteresting one. Obviously, we should pursue lots of areas of research, because the uninteresting problem will give us benefits too. However, we should make sure that we don't defund interesting projects in order to pursue lines of inquiry that will not yield results as efficiently.