There really isn't a real-world situation I can think of where I'd care about passive eavesdropping or after-the-fact decryption and not also care about active eavesdropping.
So I'm going to disagree. No, there is no security benefit to encryption without authentication.
While the impact of all these things are the same, the likelihood is not.
There certainly are real world situations where the chance of active eavesdropping (which requires a targeted attack, and is risky because it can be detected) is low, so you accept that level of risk, but the ability for someone to just grab all the traffic of a large group (that just happens to include you) for a prolonged period of time undetected is much higher.
So I'm going to disagree. No, there is no security benefit to encryption without authentication.