More or less your talking about banner exchange networks – the software is readily available. Setting up an adwords type panel of ads that could be networked would be very easy to do.
However using a PPC model the cost of such a network would be very high as Antoine pointed out for some programs the click to value ratio is pretty good.
Furthermore the bottom line is that we are all in competition to get that potential player. If the traffic is actually worth anything – WHY would you want to give it to your competitors?
Sure if your traffic doesnt convert very well then taking a few dollars per click would be nice for you, but the people paying that would quickly find out that it was as worthless as the other sites selling PPC and would stop paying you.
I think this type of exchange would have a better chance of working if individuals entered into agreements on their own with others they trusted – eg that the exchange was apple for apple and not a lemon for an orange.