Death Cart/Vineyards is nice. Clearly you wouldn't build a deck around it, but if you have a strong Vineyards deck anyway, not only does Death Cart pump up your Vineyards by 1 each time (as long as Ruins remain), but they can help you end the game since you only need 5 of them to empty a pile.
Feels like a nombo to me.
In what sense? Obviously you're not going to want to actually play the Death Carts, so it's a very late-game thing. But if you want Vineyards anyway, upgrading them by a full point for $4 and a buy is great value.
I mean as a strategy in and of itself it would
never work be tough to make win with. You would have to consistently hit 4 (or use your DC's, which has a Trade Route-Gardens anti-synergy). Each time you buy one, which will be increasingly harder to do, you would be filling in the space between seeing your Potion with more and more Ruins.
But as a late-game interaction I can see how it would be useful. I was thinking as a "those two cards are on the board, gotta rush both piles" kind of deal.