As you have noticed Guild Halls are pretty useless at the moment. For example our guild "Fallen Angels" has more than 700 members and no one is hanging in the guild hall because there is nothing to do there and the are no any benefits whether it's the smallest guild hall or 100plat one.
I think the best way to make players spend more time together in GH is by making your energy regeneration rate more by certain % This will benefit both players and developers, since players will spend more time in Guild Halls and, on the other hand, Developers can make more money since 100 plat GH will give you the most fastest energy regeneration rate.
P.S regeneration doesn't have to be extreme.. Even 1 minute off from each energy bar will keep us (players) happy enough to spend our valuable time in our guild halls with our guildies
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