Climbing on spurs was the main part of my job. I remember many winter days when I would be up there 40 feet in the air dealing with the wind. Quite a job. I had a boss that would occasionally stand at the bottom of the pole and shake it just for fun. Man I hated that.
He didnt know that I was scared of heights when I took that job...I figured it would cure that problem. The first few weeks I was almost too scared to lean back on the safety strap and let it take my weight...I just wanted to hug the pole.
Took about 6 months to completely get over my fear but it worked.
I really enjoyed that job after that...there were times when I was at the top of a pole and no one was around. Just me in the middle of the wilderness in silence.
I only did the job for about 18 months so my knees werent an issue. Sounds like you have been doing it for a long time.