The RELATED PAGES listed on the left hand column have resources to help explain the benefits of membership. A good approach and use of these is to get your club members quickly up to speed on what is available these. Get the members all psyched to recruit and have them use the tools. Seriously, is really really that hard to expect each Rotarian to bring in one new member a year???
Using "20 Reasons to Join a Rotary Club" should have enough material to make a serious impression on a potential member.