A few players find engines far less explosive in Nocturne. This isn't the only reason that comes to mind, but does anyone think weaker payload has something to do with it? The most powerful engines will usually have something better than Gold. Bridge, Horn of Plenty, a LOT of Prosperity cards, Highways, Hagglers, Merchant Guilds, Market Square tricks (technically gold but obscene amounts all at once) Bridge Trolls, Fortune. There are plenty of expansions where the deck has stronger payloads available than treasure. In Nocturne, the best thing available is still Gold, though (once you're drawing the deck, obviously). Seaside is an exception to this, but given the raw power of cards like Ambassador and Wharf, the engines are still memorable even if they only go up to double province.
Payload is probably the least important part of an engine. Trashing, draw, buys, and usually actions are all more important for making one work. But it IS the factor that turns "my deck is coming together" into "I can pick up 8 provinces this turn."