I support closing an older question as duplicate if the following conditions are satisfied:
- The older question is unclear/poorly written
- The newer question is asks a clear and legitimate question
- The newer question receives higher-quality answers
- The old question has no accepted answer, or the accepted answer (or answers in general, if none is accepted yet) on the new question better addresses the issue than the accepted answer on the old question.
Of course, merging the posts would take care of some of the issues, but why close a question by someone who put in effort to make it clear and useful as a duplicate of a lazy question that is not likely to attract useful answers?
(note: these are broad statements about questions in general, not commentary on the duplicates linked in this question)