Ride as many miles as you want, the point is to have fun on your trip. I like to cover a lot of distance on tours, so I usually average between 80 and 90 miles a day. That definitely does not leave much time to stop and look around though. One thing I can say about touring is that once you get into the groove of riding your bike long distance every day you'll rack up the miles without even noticing. This usually happens for me after 4 days or so on the road.