I don't like how he built, but I will point out that ambassador should almost never ever be ignored.
I agree, and in pretty much any kingdom where you can build an engine (like this one), I'll go for them, but I don't particularly like them, so sometimes I stray.
Even setting aside that ambassador is a factor at some point (I would think at the start, but I can see why some would think later on), you approach this game very similarly to Hunting Party + X... except you have no X. That's a trouble considering you do not easily hit $8... You hit $7 quite often.
Unfortunately, the best "X" is festival, so I doubt festival + multiple HPs would win the game, even unless the opponent is loading up on nobles.
To answer your question, I would have purchased a festival at Turn 10, 12, 13 and maaaaybe 14. Then just gain all the pieces you need over and over with the economy/+buy.
Yeah, those 7's really killed me, and I didn't think about it until just about right now, but with the Festival's +buy I could have definitely bought 2 hunting parties some turns and saved some time and definitely would have won against a try to draw your whole deck with just Nobles strategy. Oh well.