It is not essential to add extra content to your link wheel periodically, however we would advise it. Adding around 100 extra words to each property every month will help maintain the site and over time build some authority from within search engines. A great way to find ideas for extra content is through Google News which is very relevant and up to date. Try punching in your keywords and see what comes up. Once you are done adding extra content make sure you “ping” each property using a free pinging website like http://feedping.com/.