After rather extensive searching, I've found FeedWordPress. It aggregates RSS feeds into WordPress, but has some features that I couldn't find elsewhere, notably the ability to rewrite the permalink to point at the source post in a feed.

You can check it out on make.solanin, where I am feeding the blog the git commit log for the solanin WordPress network. I used to keep notes in my wiki when I updated plugins and themes, but now I can fall back on leaving decent commit messages, and have them post in a place where folks can easily provide feedback.

I think this is also going to be useful for some of my partners that have multiple sites, and are figuring out how to bring the content all together in a way that doesn't harm indexing with duplicate content (the plugin can be configured to work that out).