I think that part of the problem was I tried to combine two great tastes. And I think I actually had some pretty good ideas for how to do so, but it didn't entirely work. If I was to visit the Dresden Files in the future, it'd probably be something smaller-scale. Like, a personal RPG style thing, perhaps using the rules of the Dresden Files RPG, and following one of several possible characters and their lives. It wouldn't necessarily directly interact with the plot of Harry Dresden, but it'd be more deeply tied into the world.
Also, just to reveal some of the cards in my hand, Abby was actually part of a plot by Uriel. I mean, and God in general, to attempt to bring back Sin-Eaters in a big way to deal with the rising tide of ghosts as the Nevernever and the world in general got more dangerous. He appeared to her in an alternate form, working through local forms and local powers, to grant her the ability to banish ghosts through the ritual of Sin-Eating, which had once been prominent and important. There had once been hundreds of them in the world, to bring the dead peace as the Knights bring redemption to Denarians and so on.
But they faded and died, and so this was an experiment of sorts, working towards seeing if humans could revive this particular flame. In that sense, the fact that Nicodemus was cutting a deal with the Fiddler, was a sideways move aimed at attacking her without having to reveal himself. Because if she lived and her work continued, people would be helped. The world would become a better place, and apocalypse is a state of mind. And yet, if he went himself, then he knew that the Knights would get wind up it, and possibly other forces as well.
So both sides were playing a game of sorts through patsies. And then in stumbled Changelings, with no idea what was going on, who managed to kill the Fiddler and foil the plot.
