That's a tough one to answer. Since not everyone sees every page of every issue of the paper, it takes numerous insertions to gain enough frequency with a specific target audience for a message to penetrate. The actual frequency you need will also depend on the complexity of your message and what's being sold.
By buying from a company that's actively doing something praiseworthy, affluent consumers feel they're helping out as well-without having to do anything other than make a purchase they were going to make anyway. Find out how you can align your company with a cause they'd like to support.