The main thrust of engines that people don't get is that you pretty much want to draw your deck first, worry about doing fun things like make a zillion dollars later. Until you're to that point, all of your plays should be geared to "does this help me draw my deck* faster (or occasionally, stop my opponent from drawing their deck faster)? If no, it's almost certainly the wrong card to get. So, do I want a free Platinum in my deck? Not really; it doesn't help me draw my deck - it actually stops me from it. You don't want to start shifting your buys toward getting payload until you're at least very close to the draw-your-deck point, and quite often not until you're already there.
The only exception to that, really, is if I really need that money to get to some expensive card that will help me draw my deck - but you need pretty little money to start building that 'drawing-my-deck' engine. So I probably take the platinum turn 1 most games, but not turn 3 (by then, I already have enough money).
*By drawing your deck, I mean drawing but-not-necessarily-keeping all the cards; so if I see every card in my hand, but discard 8 garbage cards to cartographers and warehouses and hunting parties and whatnot, I am drawing my deck. Actually drawing everything is nice, but not so always-necessary.
