To me, it's the words and the combination of ideas both. Taking an idea from your fic because it appealed is just inspiration - that's how all stories are written. But if someone wrote a 'new' fic that just happened to follow the entire progression of Gonou, I imagine your reaction would be different. Fanon and inspiration from fandom I have no problems with, but there's still a line that can be crossed.

On a completely unrelated note, I can easily think of two Saiyuki authors who would AN a Shakespeare paraphrase. For what that's worth.