75 sites dang. Do a lot of those sites perform poorly, since on average w/ those kind of earnings each site would be making about $1.7/ day, which is low. Are any of those authority sites? What are the quality of the reviews like, for example do you kind of cookie cut the reviews or do you spend some quality time sifting through the actual customer reviews on the product to make your own?
I found that if you take great care in them and put your face out there so the visitors get to know you a bit better, like the ladies at only-cookware.com (i heard they make 10k/ month mostly from that site), that it makes all the difference. Lastly, what's your best bounce rate on some of your sites?