So this is definitely bizzaro day for me, because in the span of 24 hours I've not only ignored Ambassador on a board without Gardens/Silk Road (there was JoaT, Embassy, and no Villages, even I had to admit the Amb wasn't worth it), but even more shockingly I bought Thief on purpose. Colony game, we were both running heavily trimmed Bishop decks that weren't quite Golden; my opponent had more Platinums and I had more of an engine with Monument and Worker's Village and Menagerie. I don't know if it was actually necessary, but for once it was not obviously wrong!
I'm sure I overrate Ambassador a little bit. I do think that, as a general rule, you're better off overrating it than underrating it, but yeah it's not thaaat overpowering when Villages are absent, I guess.