I wrote to a few authors around that time and the biggest reply I received was from David Eddings. He sent me a thick 8.5x11 envelope with the syllabus and class notes from a writing class he taught when I asked him about how to become a better writer.
In highschool I read a book by a well known astrophysicist and wrote him an email about getting into physics. I was delighted by a page long reply that gave me some pointers and insight. It may seem nerdy, but I really learned a lot from him and respected his communication style. It's a fond memory I'll forever hold onto and hope I can be as gracious someday. As much as I wish I could be a physicist, my mathematical skills are a bit more limited, so I went into engineering instead which is also hard and involves plenty of math, but doesn't require solving differential equations as a key part of my job.
It’s an interesting story about the relationship between authors and fans, and how mundane fantasies can sometimes be more powerful than magical ones. It’s also an ultimately uplifting look at how Anthony, through his books and his advice, helped a young man through a particularly challenging time in his life.
As a young SFF reader in the 1980s, I enjoyed the Xanth series to a point but got much further into his earlier hard-edged science fiction, specifically Chthon and Macroscrope.