Adventurer is really useful in those sorts of situations. You basically are playing Chapel/Big Money sort of, with the Ambassadors serving as the Chapel equivalent... with all the coppers gone from your deck, a high density of green, and not many other terminal actions, Adventurer is pretty much the nuts -- because you do need it to get enough coin together unless you're lucky (since you'll be drawing multiple Provinces too), and it's virtually guaranteed to get you what you need (since it's probably averaging about $5 per play).