Personally I don't think that it should be the case. Why limit club guest from viewing anything else in the forum before joining.
Last time in another car forum when we did that, intake of new members dropped drastically around 80-90%.
Once that was removed, the numbers went back to normal.
Why that was the case, there were a lot of people who are perhaps new, unsure about what forums are and they enjoy going into forums as silent readers and may not even sign up with an account. Frankly I do the same with overseas forums such as E90post and BimmerForums. The moment you restrict view and access, I personally think that it is a very elitist way of thinking.
A compromise is that you left everyone have access to view all posts, etc..etc.. but if they want to post a topic or a reply, at least set it that they are required to do an introduction first before being able to do it.