A tiny bit of Googling would answer this for you. There are several studies showing that diverse groups are much (much much) better at problem-solving than homogenous groups. e.g. http://www.pnas.org/content/101/46/16385.full
Also, having more diverse groups of open-source developers makes it more likely that the product will appeal to more end-users, and also attract more developers :)
That paper has two main points in its conclusion: Our result provides insights into the trade-off between diversity and ability. An ideal group would contain high-ability problem solvers who are diverse. and also But, as we see in the proof of the result, as the pool of problem solvers grows larger, the very best problem solvers must become similar. In the limit, the highest-ability problem solvers cannot be diverse.