Reminds me of some retweet platform I use, instead of exchanging retweet, you exchange web traffic via your links.
I have a friend who created something similar to this last year, you go to the platform, pick a category of ads (widget) you want to display, add it on your blog, it starts to show the text ads based on that category, then you on the other hand can create a campaign, add your URL and link title and submit, once your widgets are generating clicks, you will be getting Points that you will use display Your Ads campaign for free. Many bloggers used it. I did too. 
He makes money from selling Credits to guys (companies) who want more Points for displaying ads (campaigns) across blogs that use the widget and he designed it in such a way that the higher the Bid (points) you place for each ad campaign, then higher your text ads will be positioned on the Widgets displayed across blogs using the widget.
I hope my explanation is comprehensive coz I was thinking maybe you tap a few things from that concept the guy used. Although he later sold off the entire Platform to some guys in India for some Thousands of Dollars.
Anyways, make it cheaper for point (credit) buyers, and sometimes dash your users some Points (sending them coupons via their mail or something) I am sure they will appreciate that and come back to use AdBlaBla more.