In reply to Ben.

Interesting idea but WordPress sort of already has this built-in. The commenting settings area gives me an option to automatically allow comments from those that have been previously approved. In that sense, you would have the necessary points to continue posting without being moderated.

The caveat is that I've also configured the settings so a comment with a certain amount of links is flagged even if they normally have their comments approved without moderation.

Love your gardening analogy. Call me the comment gardener!