I think people obviously get interpretations very wrong (as in the above examples) but that doesn't mean we shouldn't pay attention to any interpretation there's enough evidence for.
This is because if you're an author and you've written a book, you might not know the significance of it until later, or you may never realise the significance. Sometimes people other than the author can point it out because they can see the big picture a little more clearly. For instance, John Marsden has said that when he was writing the book 'So much to tell you', he didn't think that it related to his life and his relationship with his dad at all. Several years after its publication he realised that his biography did play an important part in the book. What I'm saying is that the author isn't always right in their interpretation of their own work.
Additionally, texts that were written ages ago will have relics from that era in them that the author wouldn't really have thought about including because it was so normal, but would now be quite significant for readers today and would warrant explanation. A really good example of this was The Crucible, which the author thought was about the Salem witch trials. But, as it was written in the time of McCarthyism, it has features of its context such as the fear of the unknown that was rampant at the time and people wouldn't necessarily have identified then that they could identify now.