Rentech and the other more secretive top quant firms such as TGS and PDT use nearly exclusively public data.

Funds like Two Sigma that haven't had as good (or scalable) returns are actually the ones that focus on novel data sources.

In reality, everyone in this industry is drowning in data, and the real edge comes from learning how to more efficiently parse and analyze data rather than acquiring more of it. The top performing firms work at a level where the data is merely an abstraction; above-market returns can be achieved from nothing but public data sources, if you've automated the process of extracting signals.