Indeed I wish there was a way for Pinboard to actually nudge me into looking at old links. Maybe a daily reminder like "hey, you pinned this some time ago and never looked at it since! Maybe you should give it a chance!".
I've written something like this. It's not a general service (since it would have to constantly pull stuff from pinboard), but you can run it on your own server https://github.com/gbirke/pin-this-day/