Low revenue may be due to ads which are not related to your content so less clicks as you are saying image ads are working, So stay with image ads as they may be related to your content try some other networks it will increase your revenue keep changing placement once in a time to increase CTR. Thanks & Regards - logon2future
Thats probbably part of your problem there, twiter or socnet traffic are not that good for adsense. My guess is the actuall converting traffic you used to have is actually decreased, while these freeloaders now make up most of your visitors. Do you have analytics installed? if you do have a look at the traffic source (referer).