The reason for guilds is to gather people, but also is to work toward a common goal, be a part of something and that should be rewarding; so, this is what I thought for it:

1. GUILD MISSIONS:
Some missions for guilds members that are tier based, doing these mission you will receive tokens that you can deposit in the guild hall for special, guild-based items.

2. GUILD ARMORS & TABARDS, CRESTS:
There are armors and/or costumes that are based on the guild rank, maybe to unlock with tokens. The Guild Master can have a unique armor/costume. These items can be unlocked with guild tokens. If you will leave the guild, you can no longer wear this armour/costume.

Possible OOO will add some content for Guild Hall (hopefully). Maybe they can do that any member can drop tokens in the guild hall to unlock extras for the hall.