That's true. So far, I've only got to play one mystery adventure. I had a lot of fun taking notes and trying to solve it, but that wasn't the case for everyone playing, and even people that enjoy mysteries get frustrated with them at times and just want to cut through rather than unravel the knot.
I read in another comment you wrote you were worried about people spamming zone of truth, but I feel like you've solved that in a way with your guilt mechanic. I think, if any NPC was compelled to tell the truth through magical/chemical means, that it would raise their guilt to the point of possession by the stream and they would attack the players and/or themselves uncontrollably. Which may or may not hinder the players but it would definitely be evil if they did so knowing what would happen which would be a stumbling block for some characters playing any sort of good alignment and you could make the pc's track guilt too possibly.