i've been instructing for not terribly long to be honest...only about eight months. i don't dislike it, but its not something i would want to do for too long. i do charter as well and i find myself really looking forward to those flights as i get to fly it myself and have a bit more fun.
instructing is definitely good for you in many ways and i have learned a lot, but i know what you mean. i have seen people who have instructed for too long, when they didn't want to do it and they are generally bitter and quite disgruntled about EVERYTHING. When you find yourself moaning constantly and forgetting the time when you would have given your right arm to be in the position you're in now, is when you have been there too long.
i suppose i'm not the experienced person you wanted to hear from, but it took me a while to get my commercial and i've seen several instructors who hated their jobs. they can't be bothered too much with decent pre flight briefings and the post flight briefing is non-existent.
i'm not at that stage yet, thankfully, and hopefully i don't get there, but i reckon its quite obvious when your instructor hates their job.
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"if there is no peril in the fight, there is no glory in the triumph"