I agree with ronnie's long winded post....if you are looking to make a killing from set and forget RSS feed blogs, you are only fooling yourself.
Also, I'm sure I've said this already but I'll say it again. There is more ways than just building RSS fed blogs to market sponsor feeds.
Does that mean you shouldn't build RSS fed blogs...of course not but your
if you think that those will be able to survive from SE traffic so you had better be thinking of other means to drive traffic to them.