We would get a group together at one time (on different f2p servers) to push our chat as a mature global chat, for anyone to join for chatting while they grind or whatever they are doing. We could say that it's a clan chat, but it's open to all casual and mature players, even if they aren't SeeDs. We could get unexpected interest in this, and some may even switch channels for a little bit if the one they're in is empty. The majority probably won't be in a channel in the first place, so there would be nothing to it for them.
We would talk in clan chat and get everyone talking, hopefully. The thing is that all who aren't SeeDs will still be like activity from a newcomer's perspective, and first impressions are very important. Then one SeeD will start pushing a party from the channel (on our official f2p world). We all go, and hopefully others in the chat will follow. We could drop some things and maybe have a train somewhere, then once the party starts to get tiring, another SeeD will ask if anyone wants to go PKing or something together. Then the SeeDs who actively play the game will go into the wilderness, while those of us with frozen banks will go off to do our own thing.
Finally, we would ask for others in the chat to push the chat as we did... As a chat. Say that it was fun so far, and that it can be even better if we keep pushing it. Maintain the thing where membership in SeeD is not required, and never will be required. Also make it known that we allow multiclanning, which could break the ice for some potential members.
Then later on, we can do something similar to this and keep boosting the chat.
Also, keep pushing "casual" and "mature"... Some stuck-ups may join, but they won't stay. Please trust me when I say that... A clan shouldn't be picky when it's so small and is seeking support. We didn't think about it at all in 2001, and started to end the open in-game recruiting half-way through 2002 when our numbers were up there. Look at where we were in 2003.

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So what's the purpose? If anyone can join the chat, and it's not required that they join SeeD, what would we gain? It would be fun for everyone, regardless of whether they're in SeeD or not. Events will be more fun, and spontaneous events will be more feasible. All through this, there will be increased interest in SeeD as a clan.
... And if it turns out badly, just stop pushing the chat, and maybe close it to anyone not on Ziggywolf's friend list for a couple days. The problem will disappear, guaranteed.
So what are your thoughts? It will be harmless to try, so no real reason not to do it... But how would you improve on the idea? When should it happen? Keep in mind that it may require up to three hours in total, so it's not a minor thing, but it will be more than worthwhile if it does indeed work.