The import from feed functionality was designed as a way for you to move your content to your Stream one time to get started, not as a repeated process. Of course, you could use it that way, but it will import all the content each time.
The idea is that you could use Stream to replace your current blog so that content would be easier to embed in your site (or elsewhere). Stream will become more and more powerful as we develop it, and your suggestions will help immensely. So I'll add this to the wishlist, and we'll see what happens.
When importing a feed maybe offer the option for 'no index'?
But who am I to say. I still can't get my facebook like button to work in firefox.