I think that having guests enabled in the clan chat is a good, healthy thing.
(While it can also pose its problems, it can easily be turned off if necessary)
Personally, as an active player who spends a lot of time engaged with the clan chat, if I were to be looking for a new clan I'd want to be able to see what I'm joining. I know we have the friends chat, but it is quite different, especially with the OSRS-orientated slant of the FC. Hopefully, allowing guests to join the CC means that good, active players will be more likely to want to join our community.
Just a little bit of feedback. I hope that we continue to allow guests!