I don't think anyone really uses the guild halls... I know my guild doesn't.

To make it more appealing, I think there should be a small "training area" which includes the ability to fight your guild mates, or fight dummy mobs that doesn't give loot.

Expanding more on this idea, each guild hall instance will have an NPC, sort of a guild hall quartermaster, that will give you options to enter an arena-like area and spawn X waves of dummy mobs with various options, like element type, difficulty, etc.

You can even use this to eventually have guild versus guild PvP matches with different game modes like CTF, team deathmatch, or whatever. I think it'd be really awesome. I've seen this done in other games like Tales of Pirates, and it worked out really well.