Is there a resource that ranks apps by sales numbers which might also include some idea of in-app purchase stats? It seems to me that there's a lot that isn't known from simple popularity or download figures.

The other item that could be interesting is to be able to drill down and have a view of the sub-categories each popular app "owns" and how it's competitors are doing.

To beat the Sudoku example to death, maybe Sudoku apps are popular at this point. However, what I suspect is that one might see a small handful of these apps doing very well and then hundreds starving to death.

This, to me, would be far more valuable data. If the money is spread around nicely among top apps in a sub-category it might indicate that users like to look at other options and experiment. If, on the other hand, you have five apps that are killing it and 200 that are starving, well, you probably want to stay away from that segment.