I have a site that has a great deal of duplicate content because my clients list the same content on a few of my competitors sites.
Is there any way to ask the clients to give you some additional information about each listing? That information could be used instead of or preceding the current information.
My homepage does not seem to want to pass link juice to these pages. Is it because of the high level of Dup Content or is it because of the large amount of links on the page?
How do you know this? Toolbar pagerank has not been updated across the web for about a year. I can find some of your subpages in Google. (dupe content has nothing to do with pagerank)
Would it be better to hide the content from the results in a nofollowed iframe to reduce duplicate contents
Google usually gets upset when you show content to spiders that you do not show to visitors. This is the opposite. I personally would not do this on one of my sites. You never know how Google will behave in the future.
increasing unique content with articles, guides etc? or can the two exist together on a page and still allow link juice to be passed to the site.
Increasing unique content is almost always a good idea. Again, linkjuice flows through links and that flow is irrelevant to content.
My PR is 3 but I can't seem to get any of my internal pages(except a couple of pages that appear in my navigation menu) to budge of the PR0 mark even if they are only one click from the homepage.
Many people focus a lot of attention on PR. It is almost never an issue. Relax and spend your energy on content.
I would place this site in the Campaign Based Web-App in the SEOmoz Research Tools area and see what you learn from that.