It's rare that I buy a pirate ship, but you can find a board where I'll buy it - usually with a village of some sort and a bunch of really useless actions. Your odds of getting a token just go up in a 3 player game, it doesn't increase in value *that* much (yes, some, thief goes up much more though). It's really not that good a card, you just can't open silver/chapel and trash down to a 7-10 card deck against it that is all silvers and golds, or you're killing yourself. On the other hand, if you trash all your coppers and get stewards, markets, conspirators, etc the guy with the pirate ships will never leave the dock. Or on an average board, you can get a mix, get a lot more before he has any, let him trash a bunch of your coppers and eventually a silver or gold or two, and beat him to the provinces.
Of course, the first time I ever used the card and we misused it in a 4 player game to give 1 token for every player that trashed a treasure... *then* we thought it was ridiculously overpowered... didn't take long to realize we were doing something wrong with it though.