As for the other "bad" cards listed:
* Everyone loves to talk about Counting House as hypothetical combos with Chancellor or Golem or Coppersmith... nah. Those combos usually take too long to pull off. Counting House is a very different beast: it is purpose built for beating Mountebanks and Ambassadors (and maybe Jesters)- basically, if everyone's deck is getting polluted with Coppers, buy a Counting House or three and laugh all the way to the Colonies.
* Navigator rarely shines, but in action-heavy setups, hey, it's better than Silver, and arranging your cards is useful if you're in the middle of a chain. Scrying Pool is probably its best friend.
* Stash I rarely buy. It's Pirate-proof, which is nice, and sometimes you're playing a set without any +Actions and the $5s all suck and it's better than wasting that buy on a Silver.
* Adventurer is one of my least-bought cards, even lower than Stash. Maybe throw one in a Chapel-Big Money deck? I think it's more common for my Golds to get Swindled to Adventurers than for me to buy one myself. It's just overpriced.
* I love to King's Court Harvests, no other two-card combination can get you a Colony all by itself. The problem with Harvest actually is not that it's chancy, its that a) the discard can hurt you and b) spending a terminal action just for +Coin is usually inefficient even if it's a lot of Coin. Similar to Navigator, it's best in setups which are either full of +Action and/or +Curse (because hey, that's variety).
* Explorer is sorta like Bureaucrat, only worse. It blows, and honestly I'd probably only buy it to pump my Fairgrounds. I lost to an Explorer-Duke strategy once, but that was mainly because I stupidly let them get the first six Duchies. Second worst card in the game.
* I love Bureaucrat in the presence of Dukes, like it with Gardens, and hate it most other times. It plays very poorly with other actions (since you're slooowly filling your deck with Silver), and the attack is usually minor, often a complete whiff. And it gives you no benefit this turn. But the Silvers are sufficient for grabbing Duchies and Dukes, and the attack legitimately slows your opponent if they try to do the same. Bureaucrat is way better than Explorer because a) it's cheaper, and b) the attack. I guess Explorer's silver-in-hand is a point in its favor, but the cost difference is actually really huge.
FWIW I don't think these are all the worst cards in the game: Thief tops my list, and several others (Secret Chamber, Scout, Saboteur, Moat) are worse than all but Explorer.