I think a mobile app would be nice.

I suggest have two apps.
One could have the guild maintenance and building level ups, maybe mini games to earn a litte more gold and wood.
The second app might deal with the adventure portion of the game.such as story line, arena, hall of trials, skills, blacksmith and tavern so you can stay current with leveling your character and companions. Just a thought.

I really like that idea actually... Hey, if the devs release an API, I would be happy to have a go at making an android app for upgrading buildings :)

One game I used to play a while ago was die2nite.com - They released an API for that game, and a lot of very talented players released 'apps' for the game (not mobile, but web apps that interacted with the game - but by now.. I wouldn't be surprised if there were mobile apps made for it by the players).