I'd imagine the average perpetual is about on par with Turn 1 Mathilde, in terms of magic power. Maybe a little weaker—Mathilde started knowing Shadowsteed, but I think that was a shiny the thread voted for?
Also, if I remember correctly, Johann was almost a perpetual, but his gilding promoted him straight to magister—he was never a journeyman (perhaps one of the reasons for his deception on the expedition?)
What I'm trying to say is, a person's value shouldn't come down to whether or not they are a powerful wizard. It should come down to what they can contribute to the project.
And yes, a dedicated Druid ritualist could be of much use for us—especially one who, in canon, becomes a future Magister Matriarch—but the secret history of the Druids and their Cult of the Mother is something that I feel we can not pass over. It could be perhaps the most important data point in winnowing out the truth from the superstition when we compare notes with other groups.