This board is a typical example of ambassador being bad when there's no engine to transition to. It doesn't need to be a good engine necessarily, but one has to be there. Although I don't think ambassador into treasure map would be horrible here, better than just straight buying money, which is what your opponent ended up doing mostly.
I think on this board I would have hit the barons and gardens really hard, probably forget about mine/saboteur. As it was, you could have bought more gardens, as they were worth more than duchies, and with a little effort you could have gotten them up to 5 points a piece.