Here are some ideas I have seen from other games (not graal servers)
1) A guild vault: A place where members of a certain rank can deposit items they dont use and anyone of a certain rank as well can take them, one withdrawal a day from a person so they dont take everything at once.
2) Guild games: Basing and guild sparring are the only two things you can do as a group with your guild. What if there were special guild houses built for fun, Like a capture the flag room where the leader places players from the guild on certain teams, or deathmatch.
3) Guild points reward system: Ever had a member that stands out most of all? With Guild points reward system you can give that player a certain amount of GP, of course not a high ammount that would be absurd. The GP would be taken from each member that donated the GP.
These are some ideas.