On planet.squeak.org, I use squeak/smalltalk-specific topic feeds when I 
can find them, and I omit blogs which seem less than 50% squeak related. 
I usually find the result on-topic enough, with occasional enjoyable 
diversions to euro board games etc. My model is the Debian, Gnome and 
Ubuntu planets which are about building a strong community, not just 
propagating technical discussion.

But, just send a patch or suggestion implementing the changes you want.
If a particular blog is too off-topic and there's no topic feed, you 
could try contacting the author here and talking them into line.