As a Podcaster, and this goes for Bloggers too, I know the feeling of wanting to make all my shows available to everyone. It should to be as simple as it can to get to your content into the hands of subscribers, but what a lot of people want to do is instinctively make all their old shows and posts available in their RSS feed. While I can see the value in that, it may not be the best answer.
- Limiting the number if items in your feed to 10 or 20
- Have a well organized, and easy to navigate archive on the site so people can find older shows, WordPress makes this easy
- Also, promote your archive on your show by talking it up and make sure your listeners know where to find it