If a site is pulling feed(s) and offers no original content it will not generally show up in search results after a while. If the feed is for another one of your own sites it might get you some traffic.........if it's from some strangers site I would not think sending them your traffic is the best idea in the world. I guess it all depends on your goals for your site. If you want to convert visitors into clients don't give them a darn thing to click on that takes them away from your site. If the site is a hobby site then pulling some feeds might be of a benefit to your visitors if you don't have the time to create the content on your own.

As far as page rank, it will not help you at all increasing your external links, rather you should increase your incoming links.

You should be syndicating your own rss feeds. Not others feeds.

sounds expensive...

I would never take someone elses feed and use the content on my site. But, you should be submitting your feed everywhere you can - like blog directories, etc.

It is not expensive, just time consuming to do it the first time.