He does have a point. It is a bit out of the way. A new player who has never seen secret sub dungeons (the tinker unlocks them) could miss the unlock. It depends on the area. They should program the subdungeon so only 1 wall is between it and the player (so you can see that it is there), because you'd never realize its existence if it is surrounded by two layers of walls.
We made an expansion and it is awesome. Really, you should check it out, especially if you're looking for some extra challenge.
Download over at ddmod.weebly.com!