Antonio, is it worth it for you, personally, or is it worth it for someone else? Since you aren't specifying, I'll answer both questions.
1. Is VPN certification worth it for someone opening shop that has never made pizza before?
Maybe. There are a staggering number of people who have absolutely no idea how complicated pizza making is and mistakenly assume that they can grab the right recipe and be a pro in an afternoon. If, say, someone were choosing between taking Kenji López-Alt's 'Neapolitan' recipe and opening shop with that or getting VPN training, then, yes, I think the VPN training would give them a far better chance at being successful.
What I'm saying here is that, from a training perspective, it's better than nothing. But not much. One big factor in the training equation is the person physically doing the training. 5 years ago, there were capable instructors. Now, less so.
2. Is VPN certification worth it for someone who makes great authentic Neapolitan pizza but who is looking to expand brand awareness?
Most likely not. I would say that most people who are aware of the VPN are both aware of it's shortcomings and have access to reliable word of mouth reviews. In other words, if you're going to be savvy enough to know what the VPN is, you're going to be savvy enough to generally ignore it and have alternative means for choosing a place to eat.
That being said, I've never heard of anyone say "I won't go to that place because it's VPN," and the exposure you get from VPN might give you one or two more customers. Maybe. If the price were right, I mean, really right, it wouldn't hurt. Being aware of your specific tutelage, I would probably wager that the VPN needs you more than you need them. I wouldn't necessarily approach them from an attitude of "I'm willing to let you certify me, as long it's free," but I would make them aware of your long history, your skills, your commitment to authenticity- all in the context of requiring no hands on training to be certified. You might even throw out the idea of filming your process and uploading it/sending them links so that on site certification wouldn't be required (no plane fare, no lodging/food, car rental, etc.). If it's just a matter of you shelling out a sum and them sending you a sticker and putting you in their directory, they'd be dumb not to take a few bucks for it.
In other words, I'd look at it like a yellow page ad. You might get a couple of people from it, but you're not getting anything more (regardless of what they tell you), and, since you're not getting anything more, you shouldn't be paying much more. Lowball the heck out of them, and, if they say yes, do it, and, if they say no, then move on with this assurance that you haven't missed out on anything.