The majority of my events have always been for members only. Under the free membership structure I typically instructed any non-member interested in attending one of my events to join the club first and then register. Almost all of them did and for most it resulted in further activity with the club which is key! That is exactly why we need to get back to a free membership model as soon as possible so people with even a casual interest in our group will be more likely to take the leap and join us.
If/when we return to free memberships, I am 100% in favour of eliminating the guest option. Our goal as club volunteers should be to turn everyone we meet into a member.
Also in my experience I have found people are much more committed to showing up or at least removing themselves by the deadline when they are responsible for their own registration. Guests tend to feel a little less obligated and are more likely to bail last minute leaving their friend to inform the coordinator at the event itself. I have seen this happen countless times.