After screening the content sources for length of posts, and manual selection, I was down to 1.2% of the original list of feed URLs, and still some clean-up of the content is needed. So it looks like I will use the automated tools to filter lists of blogs down to a list that can be manually edited.
I feel that it is important to have high quality content on the site, so no 100% automated solution is going to work. There will have to be manual editing of what the tools suggest would be good content.
The content that I am talking about will be blog post excerpts displayed in a widget, with links to the full post on the external blog.
So this is a way to get a big chunk of relevant text content (to the tune of around 1000 words) on the web page to mix with the text-light content of the rest of the page.