I think it takes a certain type of person to instruct full-time and not eventually want to move on. Personally I instructed for 6 or 7 years and I have to admit that by the end of it i was sick and tired of having to teach effects of controls part 1 to trial lesson punters!
If you progress thru to teaching applied Instrument Flying, Aerobatics etc it does become much more interesting. However I personally would not have found it be a rewarding or even enjoyable career, unlike what I'm doing now!
Good luck, enjoy
TJ:-)