Revenue dropped recent months even though we had more vistors and more page views. There are too many free adwords accounts out there. One day I will say bye to Adsense.
It is not really the adwords coupons or as you call it "free adsense accounts" that are causing the decrease, it is how you are optimizing your web site for adsense. The PPC you receive varies from bidder, black list any low bidding sites, optimize your site or blog to fit for better paying keywords, and remember that the less ads the better pay per ad. Test stuff out. You will not say goodbye to adsense, not many do. Trust me
But what has happened to your clicks? Visitors and pageviews mean nothing - clicks are far more important.
Optimize adsense. Target new visitors through search engines. Repeated visitors may not click on ads.