Also surprised that Goons, the card known for generating insanely huge scores, has been replaced with a card that is likely to generate even higher scores. Granted, the loss of the ability to buy Coppers for points might just balance it out; but hard to say.
As Donald said in the OP, the problem with Goons wasn't the VP-gaining, it was the attack, which didn't fit with the rest of the card and could also lock the other player out of getting it.
Regarding replacing all on-Buy with on-Gain: I personally think it's a mistake. I never had trouble remembering that Goons, Hoard, Haggler, Merchant Guild and Port only worked with buying instead of gaining. Goons and Merchant Guild reminded you with the +Buy, Hoard is rarely played outside of the Buy phase, and Haggler and Port would be obviously stupid if they were on-Gain.
The only cards where I was ever tripped up by this were Noble Brigand and Farmland. In a Hinterlands 2nd Edition Noble Brigand is probably on the chopping block anyway, so that leaves Farmland. After I made the mistake with Farmland it made sense to me why it didn't work on-Gain, but it still annoyed me in the first few seconds after I gained it and realized I couldn't do the upgrading. Meanwhile, while original Merchant Guild never confused me, new Merchant Guild actually did! I actually thought I would get Coffers for gaining anything, until that didn't work and I had to read it carefully.
I think as long "Buy" and "Gain" are separate things, there's guaranteed to be at least some confusion. The only way out is this:
MarketAction - $5
+1 Card
+1 Action
+1 Gain
+$1