Thanks to comments from my previous post, I did snag a copy of Blogert.
Just like I thought, it's almost everything that I wanted, but I want a couple of more features - like the ability to post to many blogs at once (this is my main want) and it seems from initial reaction that it would be cool to be able to post snippets of code into the entry that you're writing.
So I've got the behaviors that I want, but spread across two different apps. Looks like I've found myself a pet project. :)