Heck how can you weed them out, I think there all low paying anymore. I have never seem such a drop in value, over 50 clicks so far today, and haven't even earned $3.00. Ad subjects are mostly medical, other vary
I went through this low ppc stage for a while but it now has leveled out to a decent average value. I'm sure every new site must go through some kind of trial stage with adsense and especially important is where your trafiic came from. If you had someone coming to your site by a search and then found what they were looking for through a contextual ad I'm think adword advertisers are going to see more conversions. I don't know but google must have some kind of tracking going on...to what extent, someone else will have to enlighten.