You seem to suggest that money is a better motivator than reputation. Money is a motivator, but it's often the wrong kind of motivator. Money can bring in people who do it just for the money. Especially as the money that any site can pay for it's experts is usually much-much less than the expert earns in its daily job.
I applaud that you have created a site that tries to compensate the effort to its contributors... I just hope that you have managed to tailor the site to avoid the problems that money can bring.
Nothing I wrote suggested that in any way. You are reading a message into my words that simply isn't there. Rather, just the opposite: the top experts on WPQuestions.com have often written to me and said that the reputation that they gained on WPQuestions.com is worth far more to them than the money. More so, when they talk about WPQuestions.com on their own personal sites, they do so to advertise the fact that they have public reputation that is established on WPQuestions.com. Consider what Denzel Chia, our top expert, say about us on his own site:
"This is where I answer questions and get paid! Most of my clients came from here!"
Clearly, his reputation on the site matters to him, it's not wholly a matter of the money that he earned, it's also he's proud of the work he did and he wants people to go and look at how knowledgeable he is.
Same with Ivaylo Draganov, who links to his profile on my site from his site: http://druuf.com/
I don't think money is more powerful than reputation as a motivator, but I do think the 2 of them together can be combined in powerful ways, perhaps so powerful that people sometimes find the implications unsettling.
I do understand what you mean when you write:
> I just hope that you have managed to tailor the site to avoid the problems that money can bring
That's why the money is distributed by a vote. So that people can give public recognition to what they think was a good answer. All votes on the site are public, so if you vote $10 to what you thought was a really good answer, everyone on the site sees that you are voting $10 to that answer. It's a form of applause: a way of saying "Well Done". But votes carry more weight when they are backed up with money, rather than just being votes for something like reputation points. Or rather, votes carry more weight when they impact real world events, as opposed to those situations where they only impact a system of relations that only exist on a single web site. There are a lot of systems of voting in the world, and some impact upon real world events. Basing voting on money on a site is a way of tying the voting on that site to concerns that are important in the wider world.
As to the overall amount paid, it has apparently worked out pretty well for a number of the top experts. I cover the details in this old video from November of 2010: