[Dean C]

EtherNetFreak your test is completely redundant as you have several variables overlapping each other. You have natural site growth, natural search engine traffic, supposed vBSEO-induced search engine traffic, and you are posting quality content.

To conduct a reasonable scientific tests you'd need to isolate your variables and create three identical sites, on three different domains (and servers) and post your quality content on one, do nothing on the other, and install vBSEO on the other. Even then you could argue that vBSEO traffic is just natural organic search traffic.

The fact of the matter is, it's almost impossible to prove a certain factor has any bearing on your sites growth, other than content. After all, that is what people come for on the internet