With respect to gladiator and fortune, the big reason why buying the gladiator is good is that it can trash the last gladiator revealing fortune on your turn. This makes much easier to be the first player to get access to fortune, and often the first player to play fortune wins because the game becomes so fast at that point with doubled coins.
It is still definitely important that you are happy having a terminal gold in your deck; the fortune thing doesn't make gladiator worth it if you didn't want a terminal gold in the first place.
Buying gladiator to reveal fortune is also reasonable in non-mirror matches where only one player's deck really wants a fortune.