I think Sarah's response we the best you've received.
To add to her thoughts and your feedback;

I would consider using service Pay With A Tweet, assuming you leverage your email list good enough to where they open your email and click on your links, I would recommend directing them to a Pay With A Tweet promotion, where they can continue to your site, ‘purchase’ an ebook or other offering by sharing with their social networks (they can pay with various platforms not just tweet)

Also, I would create landing pages or the main pages to be optimized with A/B variations to test what drives your bottom line more.

Along with that, try modifying your current email’s content. Instead of covering various topics try narrowing down an email to just one item, this will reduce your click through but your sharing should increase – the idea is that highly interested subjects will have similarly engaged networks with whom they want to share something valuable with. You don’t want to engage every single subscriber in every email, but with several emails pushed with different topics you should increase sharing and even click through.

One simple great step to this is creating a targeted survey through email asking what they would like to see more of.

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