Well...I got well over 1000 hours as an instructor, and I still enjoy it. I DO think we are very much underpaid, but at the end of the day I really enjoy flying, be it by myself or as an instructor.
As with every job, when youve been overloaded with work, leaving at 0700 in the morning and not leaving the airport until 2300 for weeks, you sometimes look in the mirror and ask yourself "why am I doing this!?!"
But this is the same in most types of jobs.
Basically, I love to fly, and would do it for free if I had to!!