Steve can speak for himself, but he set up the forum to be a free and open public resource on pizza related matters. Legally, the forum is set up as a not for profit enterprise, quite possibly under section 501c(3) (as is the case with eGullet). As such, there are rules and regulations that have to be complied with to keep out of trouble with the IRS.
We are always going to have members join just to get recipes. I suspect that most people who are looking only for recipes would prefer to just search for them without being members. For forum security and anti-spam reasons, Steve has set up a system for registering new members in a way that does not pose potential harm to the forum while at the same time encouraging new members to stay for a while and contribute to the forum in a constructive way. My view is that anything that gets new members to what they are looking for faster and easier may be a help to the forum and to those members who work with new members. So, if Fidel can produce something that yields that result, that would be a good thing if it can be implemented on the forum. However, having seen well over 20,000 new members pass through the forum's turnstiles over the past nine years, and carefully observing their behavior and patterns over that time, I am not sure how they would react to a system as Fidel contemplates. Usually, recipe seekers tend to be lurkers and do not often post on the forum so it is possible that they will remain in the shadows with any system the Fidel might be able to come up with.
Peter, one need not join to browse the forums. I lurked here for at least 7 years or so before joining and found plenty of recipes. I own and operate a small webhosting company called AllSimBaseball, which is a niche webhost that hosts and supports websites that play a simulation baseball game. I have done quite extensive research on the subject of SEO and what "lurkers" do and how they behave with certain choices in front of them. Surprisingly, the majority who receive or gain access to something free and without red tape, often return to the same site at the rate of over 77%.
It is my intention to add forum links to each recipe. This serves as a doorway to more information on what they are visiting for, and the serious-minded will no doubt see the merits of joining.
That said, with respect to your observations on visitor behavior, it is likely that 95% of first-time visitors are just looking for a quick recipe and are not even remotely interested in "pizza-making" as a passion, or even a hobby. The contributing members on this forum seem to not want to share what they have easily to these "guests", unless they join and "contribute". In a "not-for-profit" situation, that is a sticky issue. But what about the other 5% who take their pizza making seriously? Do you think they will just drop by, grab a recipe and never return? I don't think so. They will lock-in immediately and faster than before because they found the site not only useful, but organized and links to forum threads will pique their interest for more.
In closing, we can't expect every visitor looking for a recipe to join and contribute. But we can expect them to return, or even bookmark and recommend the site. BTW, where are the FaceBook and Twitter "Like" buttons?