Padraig-
I know what you mean. At various times, I find myself on the course with all levels of players. Were I to point out the essential considerations around a redan hole to a guy who's best prospect is getting there in two shots, I'm probably wasting my time. However, if I find myself with a different player who is faced with a decision that the architect probably wanted to impose on a player of his caliber, I might mention something to him. Before all the rules guys jump on that last one, let me suggest that me and that "different player" are a team playing our better ball against another twosome so we're allowed to exchange advice. If I'm at a club for the first time with someone who knows about a false front to a green but fails to mention it, I don't feel good about that. The strategic considerations around a medial bunker or a split fairway are fodder for discussion.
As with any other sort of information, the other guy has to have a conceptual framework to appreciate what you're saying. Otherwise, he'll remember me as "the annoying guy who wouldn't shut up". On the other hand, "growing the game" to me means more than just a willingness to play with all levels of players and to be encouraging. It means to share some the beauty and complexities and strategy of golf.
It happened for me in an informal round late this season at Bethpage Red when the folks in my group took the time to explain a long four with a split fairway and the attendant risks with going right versus left. It can be as simple as my telling a relative newbie that many of the greens at a particular course tilt just slightly to be more receptive to approach shots and that has implications for the way putts may break.
I think it's a matter of knowing your audience and his or her awareness and interest.
Mark