In general, I expect problems that require multiple "epiphanies" - bottlenecks which require a non-obvious-approach - to benefit most from additional researchers, while problems that require holding a deep understanding of a complex and "large" problem in mind to benefit from individual geniuses.

This clearly has the flaw that true collaboration - group comprehension of a complex problem - is occasionally possible, which makes me think that focusing on solving and teaching collaboration might be more useful than focusing on geniuses.