It's true that when you're teaching students who've done most of the course you don't get to fly much. But there are enough trial lessons and demonstrations of particular manoeuvres to make up for that....so you'll get to fly. Also, as people have said, you'll get to fly WELL, and also to do exciting manoeuvres that you don't get in many other flying jobs, many of which involve flying from A to B.
On the other hand, instructing is at least as much about PEOPLE as it is about flying. You are not teaching flying, you are teaching people to fly. There's a big difference. Unless you actually enjoy working with people, and gain satisfaction from your students' progress, instructing life will be pretty grim for you and you won't be much use as an instructor. llanfairpg put it perfectly - "Its more important to learn how to handle the student rather than the aircraft, many are born to fly, few are born to instruct".