Update (because pirates like to brag):
When I wrote this tutorial, I had my war frigate and my war sloop, but I didn't have my war galleon yet. So I kept track, and it turns out that of the 40,000 I needed for the war galleon, about 15,000 gold came from plundering, and the rest of the 25,000 came from cheating at blackjack. Not only that, but I had a bit of a lucky streak, and ended up with an extra bonus 7,000 gold when I went back to use the rest of the cheat cards. I only used about 25 cheat cards (for about 32,000 gold, over three different blackjack sessions), so I was averaging more than 1,000 gold per cheat card. However, a lot of that was just getting lucky hands where I didn't have to cheat (I hit blackjack a few times), and the dealer seemed to bust a bit more often than usual. I don't think you'll always have results this good when you cheat well, I know I haven't always done that well, but you can still earn a lot of gold.
But that's why we cheat at blackjack, so we win when we have a bad hand, not just when we get lucky.
Mantaraya
Edit: Well, it's a day later (after I wrote the stuff above). I gathered up 10 cheat cards and 2,600 gold, and went to Padres to get some gold.
I lost it all. Dealer got 21 four times in a row (definitely a cheater!) With zero gold, I guess it's back to plundering! If you can't bet, you can't cheat! Arrrrr!