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All of the above are good answers, but ultimately my advice would be: make sure that the relationship between the two page versions is clear (using switchboard tags, as Sean mentioned above), and optimize the mobile version for mobile search, and the desktop version for desktop search. As others have noted already, Google has some flexibility in which signals it chooses to look at - the goal is to provide the best user experience by device.

It's absolutely still beneficial! And if it's high quality content, there's a good chance it's been building up even more authority over the course of those years. It would probably be a good idea to make sure the content gets marked "updated" or "new," though. No sense in just slipping the link in there and walking away.