I just played a game with Cache and Counting House (and nothing else exciting), and decided to give it a go. It worked to the tune of 5 Provinces and 2 Duchies in 16 turns, not earth-shattering or anything but quite respectable.
This isn't the first time I've won when buying Cache, but I'm pretty sure it's the first time that I actually sought Cache out as an integral part of my strategy, and had it work.