Re: Can we have Ignore option on topics, not boards, not users?
If I may add another possible benefit of what "ignore a topic" may offer, sometimes we want to leave a topic we're previously engaged on, either because the topic no longer interests us or it has turned into a meaningless discussion filled with spam posts. I am not sure there is currently a way to "remove" these threads from our "show new replies" page.
I have never tested it, but maybe if you deleted all your posts in those threads, it might work!? I am just guessing. If you have no posts there, no one can reply to those non-existing posts. Hence, you won't see those replies if you click the "Show new replies to your posts" button. 
Let's imagine that I want to be active in Meta but I don't want to see the above threads or some other ones I don't think are interesting to me personally. However, it makes no sense to me to ignore the users who created those discussions because I have nothing against them and I might enjoy there other discussions.
It makes a lot of sense. Ignore a person is too serious but it's right to ignore specific uninteresting topics / posts from that person (especially topics).