Let's hypothetically say that you have stumbled onto a site like this, what would you do? Chances are that you will hit the "X" button a lot faster then anyone else. Like a junk site, the visitor knows that he or she has stumbled into something that's useful or junk. To get a grasp of consistency in any type of ad agency, the golden rule to remember always is the retain your traffic. Instead of showering them with junk which shuns all of them away, think more like how you can provide something that they are looking for exactly?! With these type of blogs, they provide only irrelevant information which almost all visitors will never come back again. So let's say even if you market well on these websites and that you get a lot of traffic, the money would come at most the first day or two and spiral down to the tubes. It's good to have multiple number of blogs, but if you can't maintain them it is probably best to just do what you can like myself of just maintaining one blog. No one wants to visit a blog with no updates, so yes there are no shortcuts around it.
If you want some serious residual income, do it the safe and long way. Yes it can be a pain sometimes and at times very time consuming but it's all worth it once you get to the top of the hill. Best of luck with all of your blog endeavors!