My AdSense income is coming down as well... fortunately, I am able to sell private ads and some good referral links
Its has nothing to do with visitors.. i think there is something very wrong with your niche. If you post the website link then we might can help. Also, if you have some good visitors then you can always switch to better ppc. or some advertiser who pay per view. Since by this number i am sure you can easily get around 14-15$ (that's minimum)
It all depends on keywords. If you have a celebrity or wallpaper site, then expect very low $ per click, if you, on the other hand, target a niche like auto insurance, you can expect a few $ per click also. I had a celebrity wallpaper site with 500 UV/day...i only earned around $1-$2 a day.
Oh..that was extremely low.. if you use high paying keywords and the result is above then maybe you need to filter out some low paying adverts from occurring in your sites..