Indeed, I understand your point. However, we are tracking every click and link coming from somewhere else. When we add a new post or review, we watch to see what happens with that post or thread.
The experiment strictly revolves around search engine sourcing and word-of-mouth. As far as VBSEO goes, on another site I own, we've already shown that VBSEO improved the hit rate from people searching on Google. However, those people usually got what they were looking for and either bookmarked it or copy-n-pasted it somewhere else. It did not improve registration rate. (This site has about 90,000 posts, 130 active users and close to 2,000,000 hits per month)
We're not after truly scientific results, it's just one experiment using all of our combined forum experience to see where things go with barebones marketing & content production. We want the people that make it to our site to have come from a reference (friend/shared link) or simply a search engine. Right now, if you Google two specific words, our site pops up first on the list about 80% of the time. So, we shall see how it goes...