Uh, wait a sec, if your Goons are in play when an opponent buys something, do they get points for it?
No, because "you" in the below-the-line text refers to the person who played Goons. Or possibly the person who has Goons in their in-play area, one of those (those will always be the same person no matter what*). I'm not sure I can point to a rule or ruling that proves that, but it seems like the most natural way to read the text; and I would be very surprised if it worked otherwise.
However, Goons as Mouse-Duration
does give you the Goons effect 2 turns in a row!
I looked at the text of a few other "while this is in play" cards; but I think they all pretty much specify that it only helps "you". Except Princess, which works the same as Highway.
*Edit* Wait, maybe they won't always be the same person? I know one of the reasons for removing the Shapeshifting from Inheritance is that there were really weird ways that you could end up playing an opponent's card. Is it possible for you to play a Goons while it is in your opponent's play area already? Maybe?