Build your community.

If you have maxed out your keyword traffic and are no longer seeing an increase, then focus on keeping the visitors that you are capturing. Keep them engaged and coming back for more. Reach out to them. Get them to sign up for emails and newsletters. Work on repeat visits. Fine tune your content so that time on page grows. Make your content shareable so that visitors will attract more visitors.

I could see linking to an image file itself as useful if the image were larger and you wanted to display it outside of a paragraph of text. Many infographics could qualify for a page of their own. The site would still benefit from traffic and from authority.

Hard to beat what Dan has said here.

The only think I could possibly add is to monitor whether google has added those pages to the index, and/or removed them. I find it telling to see what google acknowledges by way of their own search results.

I agree with Jesse. Pull quotes isn't the problem. Copy article and add nothing extra of value is the duplicate content problem.

Classic answer, ..."It depends."

At one time theses links would have been considered external. But Google has grown up and realizes that most of these are internal links. Maybe it had something to do with Hubpages using sub-domains to escape the panda.

While this article is not specific to your link graph, it may help to realize that google is on to this type of linking... http://googlewebmastercentral.blogspot.com/2011/08/reorganizing-internal-vs-external.html

However, the "it depends" can come into play when you don't own the domain, say wordpress.com. Those subdomains are likely treated very differently. Each subdomain on wordpress.com is unique it's authors. Perhaps this is why Google wants to push authorhship.