I get your point. The best fic, in my mind, is written about things/issues that are never going to be explored in the show...hence people writing the fic.

Though, from what I gathered from skimming a few gen WaT fics, don't some people use them to explore a Danny/Martin friendship? While that's not exactly what I'd prefer (slash, please!), it's better than them just trying their hand at writing a case file.