One of my own blogs is quite general in scope, and recently I've started focusing on a few related niches. Unfortunately they are unrelated to previous niches the blog used to rank for.

This particular blog still gets significant traffic (about 50%) for topics that are now out of date and which are not in the niche the blog is now targeting.

Could this be affecting my very low Adsense earnings of only a few cents per click, and if so, should I progressively delete these older posts as I also add new posts? If so, will this have any impact on the blog's pagerank?