Dresden files should be about the player characters and their entanglements with the mortal and supernatural world. This scenario isn't.
You've got a bunch of characters watching a bunch of powerful NPCs doing their thing. They might be able to get an idea of what's going on in advance, but none of the the pregenerated PCs has a real motivation (or even possibility) to really get involved or interfere. Generally, it makes no difference to the story if the PCs are there or not, they are basically just spear carriers and parts of the audience.
The basic idea is really nice, the setting with the theatre is really inspiring and a cool one. The pregenerated PCs fit into the genre and setting and we had fun playing around with them a bit, creating our own little conflicts, but weren't really involved in the story. Basically what happens is the PCs exploring the locale and the other characters for a while, and then - BAM! - an unexpected monster gets thrown at them.
The easiest workaround I could imagine would be having Prospero, Miranda et al as the actual player characters (which would result in a real one shot scenario, though). Otherwise the potential PCs need reworking and aspects that really draw them into conflicts with each other and the story.
[2 of 5 Stars!]