I do not understand the point of the question. Sagan was a self-declared agnostic, and he also did a lot of work in popularizing science that might have contributed to others becoming agnostic, or at least understanding what (some) agnostics value.
Since beliefs should pay rent, in what way would the world be different in the cases where "Carl Sagan was an agnostic prophet" and "Carl Sagan was not an agnostic prophet"?
I'm with nhamann on this one. The question sounds like the kind of empty dispute that comes up in politically-motivated debates, like whether atheism is a religion or a tree falling in an empty forest makes a sound. The answer doesn't actually tell you anything you didn't already know.
Please understand that "Prophet" is understood to mean "any person that can observe phenomena over time and hazards a guess to what will happen next".
No, that's not what it means. "Prophet" means "high-status person whose teachings are worshiped as part of a religion". Attempting to broaden this term has status implications, because it's also a status threshold; lowering that threshold may be perceived as an attack on the small number of people to whom the term "prophet" is currently applied. If you want to discuss a broader meaning, it would be better to invent a new term, rather than impinge on religious terminology.
Possibly the word "prophet" should be just tabooed. But I agree that your definition seems to be closer to capturing the intuition and connotations people have when they think of the word "prophet" than is done by adsenanim.
I ask that those who want to participate follow these rules:
Syllogistic representations are preferred.
Anecdotes are welcome, but please limit yourself.
Platitudes are self recriminatory.
Haiku are considered poetry.
Math, while appropriate, may cause confusion.
If the argument that you represent is not listed above please try to limit your response for clarity.
Those who wish to argue that "Agnostic" and "Prophet" are incongruent, please understand that "Prophet" is understood to mean "any person that can observe phenomena over time and hazards a guess to what will happen next".