Hey MAHK, thanks for the post and for playing at PAX! I should bring it to the Château some time, and sign up for the beta (http://www.spyparty.com/beta-sign-up) and I'll bump you to the front of the line!
For the tells, I've identified three different high level categories:
1. "hard tells" - these are things like the bugging animation you mention, where no other partygoer will perform them
2. "soft tells" - these are more deductive in nature, and don't positively idenfity the Spy, but allow the Sniper to build a case, like the "banana bread" double agent thing...you know somebody in conversation is is, but not exactly who
3. "behavioral tells" - these are things that the NPCs do in the small, but they don't do in the large, like put a book away at the wrong bookshelf, or beeline from one mission site to another without stopping for conversation, etc.
I originally thought I wanted to have all the tells be at the behavioral level, since that matches how I talk about the game as "exploring human behavior", but I realized while playtesting that the other tell types are very useful for moderating the tension levels (as you mention, the game is a bit like chewing nails right now, stress-wise). For example, if you execute a mission with a hard tell, and you're alive 5 seconds later, you can be pretty confident you got away with it, which is a big mid-game stress relief.
For the "Action Test" golf-swing bar, it had an interesting unintended side-effect that came out during playtests, which is that at elite levels it forces the Sniper to look for overall behavioral tells, because they can't rely on catching Spies in the act anymore (or, at least they can't count on it, so it's less risky for elite Snipers to simply ignore the hard tells and to pay attention to behavior).
The combination of these factors makes the elite game much more about looking for people "acting funny" than it is cataloguing a zillion tells. Now, as I add more missions, that may change, we shall see when I finally launch the public beta soon, but I'm pretty happy with how it has turned out not to be a problem yet.
> I find myself wondering what the "time shifted" version of this game would be like
I've also thought about this. In fact, the first prototype I sent out was actually a FRAPS capture of me walking around a party of NPCs, just having conversations. I wanted to see if people could tell which character I was before I started implementing the actual gameplay. I think this'll make replays fun, because you can actually play along with the Sniper during a reply, so unlike most games with replays of the elite players, like Go or Starcraft, here you'll be able to (mostly) play the Sniper side of a top ranked game. I've also thought a bit about the async and hot-seat versions of the game, both because there's no good couch-play version of the game on a single console yet (WiiU to the rescue), and because if I do crack the async design then I could easily put it on facebook or whatever. Not a high priority, but it's worth a low priority background thread.