This question is the main reason of webmasters not going for affiliate programs. They have AdSense and they are receiving a check per month. They are earning somewhere between 0.5 – 1.5$ per thousand visitors and its fine for them (at least). But have you noticed the large drop in the Cost per clicks of these programs? The revenue is going down and you hardly see any clicks generated because of people’s banner blindness?
High ranking metrics will result in getting your site on the top position of several charts such as Top Alexa sites, Top WOT sites and so more. People usually go through these lists to discover new sites and hence you will be getting referral traffic as well. Who knows? Some of those traffic may be your next big client or loyal reader of your blog.