The Socratic Club might be a good comparison. Lewis ran it from 1942 to 1954. In his words from God in the Dock:
Here a man could get the case for Christianity without all the paraphernalia of pietism and the case against it without the irrelevant sans-cullotisme of our common anti-God weeklies. [...] Those who founded it did not for one moment pretend to be neutral. It was the Christians who constructed the arena and issued the challenge. [...] We never claimed to be impartial. But argument is. It has a life of its own. No man can tell where it will go. We expose ourselves, and the weakest of our party, to your fire no less than you are exposed to ours. Worse still, we expose ourselves to the recoil from our own shots; for if I may trust my personal experience, no doctrine is, for the moment, dimmer to the eye of faith than that which a man has just successfully defended. The arena is common to both parties and cannot finally be cheated; in it you risk nothing, and we risk all.
We have a Q&A format rather than a debating one, but there are certainly some common points. I think he would have liked the fact that this site doesn't try to be a church - which for Lewis was mainly about worship and mutual support within the local community - and is not associated with any denomination.
I imagine Lewis would not have liked the system of points and voting and badges.
I'm not sure that spiritual growth isn't happening as a result of this site existing - though it is definitely undocumented. I'm reminded of the celebrated remark of F. E. Smith (by the way, perhaps you know G. K. Chesterton's poetic reply to Smith's antidisestablishmentarianism?):
Judge: "I've listened to you for an hour and I'm none the wiser."
Smith: "Possibly not, my lord, but far better informed."
Merely providing knowledge, as we do, has its place in the total picture, as I think Lewis recognized: as he said, a key step for him was actually going to church, after a period of just reading about the faith.