So, those of you who were wondering about the whole religion-in-Persia project...
Foltz's Religions of the Silk Road is good (although the paper quality of my copy is crappy) - the right level of detail for me, and I have little enough background that the wider scope (geographically and temporally) is useful. His Spirituality in the land of the noble, although on nicer paper and seemingly exactly the right scope, is too speculative for what I want, but is well-written and recommended for those who are kind of interested but don't need rigorous citations and don't have any background in the topic.
I have a good set of notes for further research.
Also, I'm really enjoying Wendy Doniger's translation of selections from the Rig Veda.