Age Of the Answers: If the questions are substantially the same, on-topic and cover currently supported versions/or apparently timeless issues and there are answers of current value in both questions, by all means propose a merge and let those who have the capability merge them in order to improve the usefulness of the site if they see fit. Don't be disturbed if your request goes unfulfilled however.
Referal: If an answer to a more complex question refers to another answer as a step toward resolution then I would not consider that as a merge candidate.
Bad Plan: As I have yet to be faced with the task of merging questions I can`t answer this with a great deal of confidence, however I do believe that canonical Q & A's can be a highly effective way of providing quality answers to common questions in an efficient manner.
Edit: a review of Moderator Tools - Make merging questions a little easierModerator Tools - Make merging questions a little easier seems to indicate that merging is not only a bit convoluted, but in most cases a really bad idea with many details to consider. I take this to mean that unless the candidates are identical in virtually all respects (including specific details in the answers) it's probably better to just mark as a dupe.