Consider this scenario. I run into an issue and put together a detailed question. I get a few answers but no luck. It turns out it was a complete red herring, and it was a completely separate unrelated problem that was causing the symptom that was in the quesiton.
So given that the question is not really relevant. In these cases, I would go and delete the question given that it's not a valid question. My concern is that I would like to notify people that were looking into it instead of simply removing it under the covers to avoid anyone wasting time trying to help answer.
What's the protocol here? Should I put a vote to close my question? Is this not a good use of "delete" for questions?
Even breadcrumbs are useful.
Your questions and the answers they spawn are not just for you, they are for the community at large. Keeping a valid (yet personally irrelevant) question around is vital to getting answers for the community problems.
If that means answering your own question with why it turned out to be y instead of x, then that's ok too.
You could always answer your own question explaining what was actually causing your problem.
If I am having the same problem as you and come across your question, the fact that you posted what was actually causing the problem could help me too.
The only time I voted to close my own question was when my Google-fu failed me and I managed to post an (almost) exact duplicate on SU - I just used all the wrong keywords while searching for it.
If it's a really really specific question, and the solution was completely unrelated to the symptoms (i.e., the question has no value to anyone else, now or ever), then deleting is fine, or flagging your own question so a mod can close as "no longer relevant." If it gets closed, consider adding a comment of why you chose to have it closed.
If the question is generic enough that the discussion could prove useful to someone else, then there's value to leaving it open.