I don't know how useful that really is. The experience tells enough, I think; you can't get high experience without plenty of votes. Granted, there are other means of gaining exp, but the primary one is and always will be rep. So, if you just say rep = exp*3 (the chance of your exp being affected by a vote, from the Voting/Experience System node, is 1/3) you won't get a perfect number, but it'll be close enough for your stated purposes. Another clue is to keep a lazy eye on the Best Nodes page; if someone's consistenly showing up on the "Best of the Day" list, then that's a good indicator. If they're consistently showing up on the Worst Nodes page, that's a different indicator. And if they're on the Best/Worst of All Time, that means they got one really good/bad one; it doesn't necessarily say anything about the quality of their average post.

- Ozymandias

Update: I just tested this theory on my own Home Node, and it works, more or less. The estimate (calculated average rep/node) was off (high) by about a point. So for rough guesstimates of "how good" a fellow monk is, this is good enough.