My question for these new would-be quants is, how do you see your work?

I know there are certain types of smart whizzes who see working for Google/Facebook/Amazon as some sort of intellectual step down, or where in finance the value to society is some handwavy "market-making" argument (depending on how philosophical you get), but presumably these types going into this are also tenure-track, research producing scientists. You could spend your time disproving the Higgs at Cern, or you could optimize pennies (albeit in ever more challenging ways).

Have these Renaissance/TwoSigma type firms really ever delivered social value that isn't a new trading model with a limited shelf life? Is there new tech? Network, hardware, software innovation that spills over into the real world?

You can read more about it here, too: http://beakernotebook.com

Jane Street is also pretty awesome - they open sourced their in-house standard library for OCaml, called Base: https://github.com/janestreet/base (they use a lot of OCaml).