Duchess seems like an obvious fix to me. I'd make it so that you couldn't buy it, but you could gain one when you bought a Duchy. I'd make it just +$2 and +1 Action. It encourages 3 Pile endings to go for Duchies, since buying Duchies is faster. It just seems like an interesting strategy to go for in general, I dunno.
In two player, there are only eight Duchies, making it impossible to drain the Duchess pile without buying them.
Also I feel like its terminal aspect makes it really more of a decision whether or not to go for it, rather than its presence just meaning "get a free Silver with every Duchy".