When I see similar questions which I can't or don't feel like closing as duplicates, I usually post a comment under one of the question with a link to the other one. This makes question *linked* - I don't know all the implications, but the obvious one is that both questions get hyperlinks to each other in the `Linked` sidebar. This improves navigation without any ethical implications that voting to close might have.

Having said that, if your self-answer covers an older question better than its own answers, I advice you to vote to close and let the community decide.