I'm also interested in the design process with these cards.
Say you have a card which is simply: +4 Cards, +1 Buy.
Now you're thinking "how much should it cost?"
If you make it $5, it's too strong compared to Smithy. Just $1 extra gets you both a Card αnd a Buy?! Wowza! Going from 3 to 4 cards is a pretty big deal and the buy is just icing to make the most out of your huge hands.
Okay, so maybe it needs to cost $6. But if it does, well, maybe it has the Adventurer problem of being too expensive for its own good.
So we end up at $5 with a card for each opponent.
Now, along comes Hunting Grounds, which originally was considered as: +3 Cards, +1 Buy (with the trashing part) for $5. The trashing part is cute, but doesn't come into play all that often I think. Apparently Donald thought that getting an extra card and giving one to your opponent was roughly equal (he still did with Governor). I think giving a card to your opponent is worth a bit more than getting one extra yourself, but okay, I can understand they're roughly similar. So Donald ended up switching the Buy out for an extra card and making it $1 more expensive. Personally, I think the +Buy is worth more than the card when you're already drawing 3, but oh well.