My former prof switched university and now I can't ask him in person for a LOR - should I try to see him?

I don't think a visit is necessary (and I don't see where in the linked thread it says otherwise). Even if you were to visit him, you would contact him first to make an appointment, presumably by email.

Why not send a mail in which you both ask for a letter of recommendation and whether the prof would like to talk to you to refresh his memory (be it in person or on the phone)?

The question you link is about getting a letter of recommendation from a professor in your own university. In that situation, it makes sense to talk face-to-face. However, when the professor is in a different city, this is no longer necessary or even reasonable.

Honestly, I'd find it kinda creepy if you arranged a meeting with me and the smalltalk went

Me: So, how come you're in town? [Thinks: probably visiting friends or something and just dropped by because they were here.]
You: I spent two hours travelling here just to talk to you for fifteen minutes and, when we're done, I'm going to spend two hours travelling back.
Me: [Thinks, er, how do I say "You know about telephones, right?" without sounding like a jerk?] Um. ... ... Ookay.

If he is someone who is likely to write you a good LOR then he is unlikely to be annoyed by an email asking for that. Traveling there seems like overkill to me. On the other hand, if it is really, really important to you then it is unlikely to hurt to ask him in person.