Introduction: … and this is the opinionated Mr. Smith.
"Opinionated" seems like the word I want to use, but it and its synonyms all seem to have negative denotations or connotations.
Is there a nice word (or very short phrase) to describe someone that has a considerable general knowledge and experience, and is able, whenever asked, to offer an opinion on almost any topic?
UPDATE: The answers so far are close, but miss the idea that the person enjoys giving his opinions and ideas (but does so only in appropriate circumstances).
In terms of real people, I'd say Isaac Asimov would be a good example. He was knowledgeable (or could quickly become so) on any topic, and never missed an opportunity to provide an opinion.
(And no, I don't want "Asimovian" as the answer.)