Dosh Dosh has a great post about 6 Fool-Proof Steps to Make More Money With Your Website. It's well worth taking your time to read it. Here are the 4 desired outcomes of taking these 6 steps:

1. Monetize. Get more (or some!) revenue out of each post.
2. Capture Leads. Encourage a visitor to subscribe to your mailing list.
3. Improve Relevance. Provide an improved user experience for all.
4. Make it Rank Better.  Doing on-site and off-site optimization will help specific money pages to rank better on the search engine result pages.

Each is a great reason for optimizing your most popular pages. Give it a read and try to implement the suggestions. They're worth doing.