Ferry is fantastic.
I can imagine a board where it doesn't make sense to open Ferry on 3/4 (no +buy, no 5+ cost cards worth having in bulk), but I've never played such a board (I've probably played with Ferry ~10 times). There are a few cards that make Ferry especially bonkers: Stonemason, Goons, and Grand Market come to mind. The interaction with Goons is a little unfortunate; a player who opens 3/4 (as opposed to 4/3) has a significant advantage.
I expect that Ferry + Workshop can be a trap sometimes. Suppose there's a board where Margrave is the only source of draw (and there are other components to make an engine). I would definitely prefer to open Ferry + Margrave over even Ferry + Ironworks. The early Margrave can help you spike a double Margrave turn almost as much as Ironworks, it cycles you faster, and it attacks. On the other hand, Ferry + Grand Market is greatly aided by a Workshop-style gainer. Then there are a bunch of cases that are less clear.
Moving your Ferry later (after the first pile is empty) is often correct, I'd say; especially in the presence of +buy. It only takes two purchases of the new card before you've made your money back (and more).
Ferry is super powerful, but it doesn't do anything by itself. Like Chapel and King's Court, it empowers the other cards in the kingdom. The only time I've been sad that Ferry is in the kingdom is when it further powered a game-warping card (e.g. Rebuild, Cultist).
Aside: I guess I'll have to create the thread for Alms later this week, lest everybody forget it and the three other skipped events.