First let me say "nice idea"...however, I think there is a fundamental flaw in that you are equating XP with "knowledge" when it actually has no real relation.

Monks can obtain XP by doing nothing other than showing up and/or voting. Clearly this would give no real indication of their overall knowledge of anything other than how to login and use their votes. ;-)

The other issue is that some monks get more XP just because of who they are....does a point by merlyn or tye hold more value than one by any other monk? Well, perhaps....but I often have observed spikes in reputation just because of who posted it, not because of what was said.
I have also seen well said posts take a dump because of a counter post as well so clearly, reputation is usually but not always a good measure of quality either

The other flaw I see is your assumption that Monks will be altruistic enough to say "hey, I really don't know enough to advance"....I think the realities of status and greed will keep this from ever working.

The last point that should be made is the most significant...while getting XP can be fun, it doesn't mean anything. As has been previously said here before...XP has no real value.

Still, I gave you a ++ for the original thought, even if I don't see if being very practical.