Technical things first: I think you want this to say "worth 0 VP" somewhere; it's a VP card after all. Also, in order not to get a ridiculous stacking effect (unless that's what you want), you could maybe change the wording to: "At the end of the game, count the VP of all your VP card that are not Wonder. This is worth the amount of VP you counted."
As for the card: I think the on-gain effect is too harsh. That way, this card basically costs $16 (a Province + $8 from this), and you have to have the Province in hand in order to be able to gain it. And you're right, Swindler is a big problem.
One alternative penalty I can think of is "when you gain this, trash all cards you have in play". This makes Swindler less of a problem (there's an interaction with duration cards, but that's not too bad). It also has an effect that once you get your Wonder, your deck is crap, so it's only a good buy as a finisher. It also mimics sacrifices, maybe even better. Megaturns might be a problem, but not really a bigger problem than a megaturn piling out the Provinces.