This is the opposite of the standard newbie Goons question.
What in the rules makes it clear that, when you have multiple Goons in play, you get multiple VP per buy? The card says "while this is in play, when you buy a card, +1VP". The correct interpretation is that if you have two Goons in play, the +1VP effects are cumulative. But what in the rules (other than the Goons FAQ entry, which does make this clear) rules out the non-cumulative interpretation:
"This card tells me that while it's in play, I get +1VP for buying a card. This other card also tells me that while it's in play I get +1VP for buying a card. I guess I definitely get +1VP for buying a card, then!"
I'm asking this because of the often-stated principle of Dominion that the card FAQs should be redundant; everything you need to know how to carry out the effect of a card is on the card itself and the main rules (and expansion rules). Do the rules clear up this ambiguity? There are a couple of other cards which could be subject to the same misinterpretation—Hoard, I guess?