Not sure if there are any widely published authors, but like you, LEGO castle has inspired me and much of my writing (for several years, actually). Recently, I have been trying to write something to my story
everyday, because it can be easy to get a bit lazy and stop writing after awhile.
Anyway, as Maedhros mentioned, Castle World
exists as a LEGO story writers forum, and CC has had several very interesting RPG stories written by members here, as well as some good stories written in the stories forum (I'm moving this there now).