My take on the health benefits of coffee or tea is that it's probably nothing to do with the caffeine, and a lot to do with antioxidants. Both of these drinks are high in antioxidants, and the typical modern diet is low, so for a lot of people caffeinated drinks are a major source of their antioxidant intake. This shows up statistically as coffee and tea increasing longevity, but on an individual level, just make sure you're getting antioxidants from other parts of your diet instead.