Frankly, I feel that I've gotten more out of most of my posts than the sum total of all those who have read them; the questions posted here inspired me to dig into the documents and figure things out for myself.
I think this is a very common response, and I concur with it wholeheartedly. ("I knew I should have concurred ... why didn't I concur?" -- a loose quote from my vague memories of Catch Me If You Can.)
One of the things that makes PerlMonks work is that it is not a zero-sum game ... the time I spend at PM is often the most productive part of my day. The two minutes someone spends dashing off a quick reply to a question can potentially have a hundred-fold return for the OP, and the ripples spread throughout the monastery.
Another contributor to the success of PerlMonks is proper self-perception, or humility ... I think that a lot of the high-XP monks continue to benefit from the other members because they don't fall into the trap of thinking they have all the answers. I know that I come here more often to learn something I didn't know I needed to learn, than to get an answer for a particular question. There is, after all, more than one way to be a PerlMonk. :)
No good deed goes unpunished. -- (attributed to) Oscar Wilde