Ok, then, to *re*-read Ars Magica
Atleast the magic system. And I agree about the later editions, I didn't find the last one I read to be nearly as enthralling as the one previous.
As far as Venice goes...well, probably not thieves or bandits, unless they're of the mer-variety.
Titanium burns just fine, too.
You wouldn't necessarily use the "domains" the same as are currently implemented in Ars Magica-you'd definitely have to extend and warp the concept, but the underlying idea is there and could be made to fit Dominions.