Hi Jason,
Sure, I use what people send me to learn from. Matter of fact, I keep a swipe file of newsletters, sales letters, etc ... so I can refer back to them time and again. They are like case studies if you know how to use them when Internet Marketing or marketing in general on and offline.
And there are things you can learn what not to do from some lol.
Remember me talking to you about how to gain the best niche info and what is the hottest by using your site? Well, simply apply the same info using other people's newsletters.
BUT, I would deffinetly write original content for your list and sites. In other words, it is okay to take the main niche and idea as a focus, and then put your own spin on that info. Now if someone maps out a specific type of plan that you didn't write, but want to use, for goodness sake, don't steal their work and tell your list you wrote it. Give the original author credit for it. You may even want to ask their permission to send or forward the info to your list promising to give their name and perhaps a link back to their site.
What I am saying is, there are right ways and wrong ways of using information online to your advantage. Most importantly though, is to use it and keep your reputation in tact.
Good solid question though as people will learn from it too.
Btw, original and compelling info is hard for most people until they start writing, and after a little while, they get better at it. Lol you haven't been writing your own stuff for very long. Keep writing, and you'll see first hand what I mean.