Well, being a relative newbie here, perhaps I have no right to chime in, but being a bit of a gadfly...I'm gonna do it anyway.
From my perspective, once I purchased a KF vehicle it was obvious to me that if I wanted the most immersive experience, then joining the club was the only choice. I do understand there are others who do not see things that way. However, as someone who has moderated a forum or three in my past I can tell you that limiting access to a forum does not raise its paying or contributing membership...if anything it drives said potential revenue down.
After all, how would a potential new member know if joining the club for access to the forum would be beneficial to them if they can't test drive the forum (to use an analogy we can all grasp)? There will always be people who join a forum just for access to the info and ability to get their questions answered...getting something for nothing is not an unknown human trait. But to close the forum to anyone not a club member just assures anyone on the fence will likely just climb back down on their side. To some it would appear churlish and money grubbing...to others it would simply be a matter of having no idea if joining would have real value to them.
I think some excellent points have been made for keeping the forum open, or at least having it open as read only unless a member.
But I think the best reason for keeping the forum open is the many fine folk here who will go out of their way to help. I'm sure a few of you are sick to death of the many questions I've asked since my arrival...some may even wish that I'd just go away...not mad, just away. But it's all of you who assure I will be a member of both the club and the forum, at least until such time as I am room temperature.
Personally, I couldn't see being here without being a contributing member. The number of people still interested in older cars like this dwindles by the day...younger generations, at least many of them, could care less about these older beasties, so I think it's incumbent on those of us who do still appreciate the history, grace and styling of these vehicles to do our part to keep the wheels rolling down the road, so to speak.
To conclude, I can only offer a simple adage which is and always will be true: You can catch more flies with honey than with vinegar.