Our guilds are very bare if not as useful as the Haven Hall.
I'm pretty sure allowing guild officers decorate their guild has been suggested. How about a guild pool/treasury? Group members can dump crowns/materials (the kinds of materials may be limited to 3* items, at best). If there is enough crowns/materials amassed, officers can go to a special alchemy machine and craft a random prop/furniture of their choice!
Think of it: A bone throne (or a pile of bones), gloops of jelly, a tree found in Stone Grove (I WANT A TREEEEEEEEE), any of props you might see while adventuring in Cradle!
The guild alchemy machine will work like equipment AMs, except you don't need to buy any recipes because it's "already programmed" into the machine.
And once you dumped your crowns/materials in you can't get them back, even if you're an officer. This is to prevent officers from stealing the funds.
Thoughts?
What I suggest is the following (Using parts of your idea):
1. Guild Bank - Players can store weapons (Any type 1* to 5*) in the guild bank, but a maximum of 10 weapons, armor (Helm and Body), and Shields. Then guild members can go to the bank and withdraw the item for a timespan (Which the person who deposits the item picks 24 Hours to 96 Hours) Finally, the guild member who deposit the item is repaid by any heat the item gains during the period it was withdrew is kept on the item. Why have this? Lets say I know for a fact I dont need my Divine Avenger or a guild mate wishes to test out a Divine Avenger I can let them withdraw it and test it out, or if you have guild members just starting out in the game, and you want to give them one of your weapons or such to well give them a slight advantage.
2. Guild Hall Furniture - Okay for this my idea is simple have the guild members put crowns into the guild bank (Once put in they can not retrieve them back), the crowns are then used by the Guild Master to buy furniture and such for the guild. (Example: Have Guild Colors (Banners which are different colors) Guild Chairs with an option to sit on if not too complicated, Small arena (Which would cost tons) where players of the guild can go into and fight each other for fun, and whatever else you guys come up with).
Side-Note:
I have been hearing a lot of talk about players wanting to have gates in the guild hall, and I do not think this is a great idea. Only because this being a social game if players are just hanging out with guild members and well basically hiding in a sense from new players etc. This could make it harder for new players in the game to well get to know the players and lead up to a game which is not real social.