Several members of our team here at Thrive attended Hubspot's Inbound 2012 conference in Boston at the end of August. After attending one session in particular, it occured to us - we have great content but if it doesn't work in one format then we need to change it. Maggie Georgieva held a session all about whitepapers, ebooks and how to repurpose "old" content to make it fresh and new. She said content that has already been published can be used again when you redesign the way in which it is delivered. For instance, if you have written a whitepaper and created a landing page form but saw little interaction - you can tweek the content to hit a new audience.
Maggie made a good point about the issue of content not reaching all your desired customers - repurposing could be the difference between getting a new lead and not. Add enhancements to your original whitepaper, rewrite the paragraph on the landing page and rework a new email to your list proc. Sending an email will let your customers know that you are working on new content for them and explains the benefits. Emails are essentially the ticket to get someone to fill out the form on a landing page. There is no rhyme or reason behind a design of whitepapers or ebooks - yes you need it to look appealing and enticing but there is no rule that says your document must have certain design elements.
Take your "old" content and combine that with another similar topic of content and compose a new whitepaper that your customers will love. Be sure to stay within your style you've created for those documents but make sure that you catch the audience you want. Design your documents with the content and customer in mind. If you were the customer, what would you want to read? It might not hurt to ask. Send out a survey...you might be surprised at what you find out.