But why allow users SO users who aren't part of SU to vote to migrate questions here? It is clear that they often are not competent to decide if question would be on-topic here or off-topic here. I think it would be smart to allow migrate option if and only if user has X reputation on site to which question should be migrated. X should be a low number, probably under 1000, but high enough to be a proof that user is aware of basics of the other site.

The problem with this approach is that it shows up for all questions which have an answer or are past certain number of views. In my case, I have several question which do not have a good answer and appear red. I think that there should be a different type of notification if there are answers with lots (say 5+) of upvotes. Even better! There should be a separate section with questions which have unaccepted answers with large number of upvotes. This way user could at a glance see all possible candidates for accepting answers.

+1, but there/their errors should be fixed

That's OK for this one particular question, but do you think that's the correct procedure in general? It'd be nice to have a reference for future cases.