Thief in 2P has even less use than Scout. Scout at least does anything nice for your deck instead of clearing out your opponents coppers. (Although both are, most of the time, inferior to Silver) Even Transmute, one of the slowest cards in the entire game, has it's uses, especially with more Alchemy cards on the board. Thief isn't even a good buy in base only games >99% of the time. Sometimes against Chapeled decks it's okay, but even that are rare cases.
In games with more players, Thief becomes better and Scout will replace Thief. I also think Counting House is... pretty bad at 5, but there are situations it can shine at least.
And I think Adventurer is okay. Not "I will but it many times over gold"-okay, but in a deck with much junk it's pretty nice. Providing you can get up to 6 with much junk anyway.