I bought "Dr. Strange" the moment it became available on iTunes (where you can actually physically own a movie instead of merely owning a license to watch a movie), and I now realize that the movie does indeed answer one of the questions posed in my review:
Librarian Wong notes that sorcerers must never interfere with the flow of natural law, which is what makes playing with the timestream so hazardous. During the wizard-battle sequences, reality is bent and twisted and fractalized in all sorts of different ways, but we mere mortals seem not to notice when our cities get turned into toroidal landscapes, and our streets become Escher-like constructions with the world's most bizarrely impossible traffic patterns. (This is very much like how magic operates in the world of Harry Potter: Muggles, i.e., non-magical folks, are blissfully unaware of the powers at work around them.) So my question is this: how is all this reality-bending not a violation of natural law?
The answer is that the city-torquing sequence in question takes place almost entirely in the Mirror Dimension, which is layered over our normal reality but doesn't directly affect it. Think of the Mirror Dimension as a universe-sized arena in which to perform magic safely. The zealots, led by Kaecilius, gain more power in the Mirror Dimension because they're drawing power from the Dark Dimension (however that works), but the effects of that battle don't leave the Mirror Dimension until the Ancient One is stabbed and flung through a portal back into our world, where she falls and is mortally injured.
So! One question answered.