On the level of mutual inspiration and shared interpretations, I definitely agree. It's not possible, in any case, to avoid similar plots and events, given the fairly narrow range that any canon allows (if you're going to stay in-character and within the canon cracks, that is). I enjoy seeing how different writers make use of the same plot or trope, for instance -- as you say, the "shared sandbox" is a great deal of the fun.

But while there is a fairly wide scope for allowable sharing, it's the line-crossing that I worry about -- the stuff I consider actual plagiarism, not just inspiration/retelling. I know the line can be fairly blurry, but there's a difference between inspiration/homage, or saying "X happens in so-and-so's story, and I'm borrowing that event as canon, or "here's my version of such-and-such convention" and the sort of borrowing that is unacceptable. It's the "unacceptable" that I worry about.