My vote is to not restrict guest access, at least not totally. In this age of too much personal information solicited on the internet; identity theft, scams, and spam I don't do anything official on the internet and I jealously protect personal information. From this mindset, if it had been necessary to provide personal information, such as name and/or email address, to register before I could have sampled this fine forum, I would have passed you bye.
This forum already restricts guest access to some of the features. For example, a guest cannot post, a guest cannot access the "At The Handle" section, a guest cannot access Bob Hunt's vendor's site. I would offer these suggestions. Do not totally restrict access to the Open Forum. For a guest, maybe limit the access to topics older than 30 days. I am not sure if a guest can search for a topic or not. If he can, then restrict this. Some access to the Open Forum is the Forum's primary means for enticing a guest to register, in my opinion. If you can restrict access to other sections of the forum, as you do with "At The Handle" and still have the name visible in the index, do that. At least a guest will be able to view the titles of other sections that may be of interest to him and, thus, be further enticed to register.
Personally, I have not found the very few occurrences of slow response, no response, or site failures of one form or another to be a problem.
Joe