How about:
Dear Mr. Spinney,
You were such a positive influence in my life. Your performance of Big Bird has enriched my being since I was a child, and has continued to do so to this very day. Even though I don't know you personally, I consider you a dear friend, and a mentor that has helped shaped me into the human being I am now. Thank you so much, you rock very hard...and I Love You
Sincerely,
<Your Name Here>
You can use whatever of that applies to you. And BTW...it isn't wrong to love him!!!

(I think we all do)
-Matt