So, with some work and some arguing, I managed to schedule my Final Offering session for the Open Evening and gave it a shot. The second time around, things went much more smoothly. I played down the depth of the NPCs, played up the interesting factors surrounding the demons (the fight, this time around, was much better), and I kept the pacing swift. We, in fact, managed to finish the entire session in just under 4 hours, which is an excellent clip, and it left nobody feeling underwhelmed. I had a player who played in both, and he felt it was quite an improvement and, in his words, "probably the best session I'll ever get out of an open evening." Strong praise.
I still feel that the sandbox model I've developed works best for campaigns or "long-shots," multi-session one shots. I end up feeling as though I'm missing alot of the nuance in my game, and thus all the NPCs get a glimpse, and then we move on (a female player expressed interesting in Gill, surprisingly enough, but I lacked time to even touch on him further). I think I can learn some solid lessons from this (that I'm at my strongest when I design characters and then work a plot around them, rather than the other way around), but it's probably a model best left to my longer games.
Amusingly, we had very similar events in both games. Zig-Zag, our assassin, opted to be a janitor once again, and got in a seriously lethal, though not killing, blow. A female player chose Shadowheart and played as a student, fell in love with Dixon, and used Corpse Witness on a dead pigeon. At least this time, she got to speak to the Pigeon King and, erm, make-out with Tom-Tim (Who is now her favorite spirit character evar). All in all, an excellent session and a big improvement over the first time around.