[Core Engine: The World Behind] A Second Thread about my Magic system

Justin,
Have you read Authentic Thaumaturgy by Bonewits? He's a real-life practitioner (whatever that means) who put out a book designed (in part) as an RPG resource, and he provides a nice list of "Laws of Magic". I can quote them for you if you're interested. Personally, I found them so purely conceptual as to be somewhat hard to mine for gameability, but it might be a fun comparison of perspective to your own.

As for immersing in magic-use, my favorite way to create that is by ensuring that:
a) doing something magical requires multiple steps
b) none of these steps is a guaranteed success
c) none of these steps provides the same experience every time (boring!)
d) the whole process is given striking color in some affecting way -- visceral (nudity, blood, urine), taboo-violating (cannibalism), cultish (dancing, chanting)... whatever your game's aesthetic is, magic use should represent that to the utmost degree

My sense of Vertigo comics' urban magic was that it was all over the aesthetic map... Mad Hettie snapping a stick to break someone's leg and then doing auguries with tea leaves and dove entrails, Constantine having continuous "lucky coincidences", dreams affecting reality and vice versa... It was more just magic done by urban people in urban locations. All this is just my opinion... I just hope you have some distinct aesthetic in mind; otherwise, in my experience, players will just want to hurry up and resolve the spell effects.

One option, of course, is to make the steps of casting dangerous (or otherwise consequential on some large scale of play) instead of just non-guaranteed-success -- that'll generate an immersion-fostering level of concern and attention better than any color.