Mine was as simple as it gets: a list in Reminders, recurring reminders every 2 weeks/1 month/3 month depending on how close we are/how frequently they have interesting things to say.

If I see the reminder I try to call/text that person when I have some down time. I tick the box when done, or if I think I've seen talked to them organically recently enough.

I'd be cool if it could somehow tell from my call/whatsapp log/calendar how long it's actually been, but it being a fuzzy is a feature too.

And as you say, definitely worth it.