It could be that prestigious second-movers deserve the credit if they are responsible for getting people to pay attention to the previously neglected topics, and possibly we already credit first-movers more than we should (which is why I said "optimize for academic fame" instead of "positive social impact"). Which brings up a question: what determines the topics that academia pays attention to? If we had a good model for that, maybe we could use it to generate some munchkin ideas for making it pay attention to important but neglected ideas?