I blurly remember that in Darkening of Mirkwood there's a mention in one of the years to a second Gathering. But as the Darkening is beginning, not all leaders attend (some have their own problems at their frontiers) and it's a powerful way to underline for the characters that all those "brotherhood among all folks" are gone. Specially if they attended the first gathering and, afterwards, learn from the problems of Beorn with the Viglunds, Thranduil with the spiders and the issues with Bardings lumbering in his forest, Mogdred and the Woodmen, etc.
Wilderland has once again succumbed to the isolationist behaviour of all kingdoms, and only some actions by the heroes manage to get them together once in a while from there on.