My adsense revenue has been falling too, despite rising traffic and more clicks. The EPC is just dropping.
So I tried Yahoo and found it significantly worse. The EPC is higher, but the targeting is so poor and the ad quality and relevance so low that my click through ratio dropped by a factor of about 5 giving me about 50% (at best) of my Adsense earnings.
I'm now building up affilate sales earnings and that's slowly generating more and more revenue.
I suspect the best days of Adsense/Yahoo type programs are behind us.