I really like (Generous) Benefactor, but it has a timing issue. When exactly do other players receive the extra $?
I assume it triggers at the start of the players buy phase. Try for a rewording:
"While this is in play, at the start of any other players buy phase, if that player has no Gold, Platinum or attack card in play, he gets +$1"
Neither this nor the original wording will work. You won't have Gold in play at the start of your buy phase normally, you'll play the Gold after that. The only way I can think of is to reduce the cost of cards as long as no Gold is in play. And I wouldn't include a platinum on the list, because this set doesn't have platinum in it.
Also, it looks like it could be balanced without giving anything to the other players. Terminal silver with no extra bonus now, $1 and a buy next turn. I guess the closest comparison is to Merchant Ship, but the $1 instead of $2 next turn is huge. I mean, look at Fishing Village and lighthouse; they only give $1 next turn, they're non-terminal, have other benefits, and cost WAY less than Merchant Ship.