Think about an "test server" type option. Maybe a PCG button on the UI you could click to pull up a list of this month's PCG dungeon. I like PGC dungeons to be "test" dungeons in which players play through the the content with no loot rewards just to try out the content. At the end the players rate it. Each month the few highest rated PCG dungeons are taken by GW to be given a GW makeover and added to the game.
1) It would give players an out let to be creative.
2) No risk of anything server imbalancing happening - no loot just the fun of playing through and figuring out the puzzles and encounters.
3) Give players something fun and free to do if they would like to.
4) Give GW a supply of new content that the players have already rated as content they enjoy.