edit: it looks like tC may have had a change of heart on this issue, so this longwinded post of mine may have been unnecessary.
terminalCopper, I think this is a strong article, and I'm sorry to be harping on this one point.
I believe the general point about +buy that's being made here is that lack of plus buy makes saving your extra money for later more useful. When there's no +buy, it's harder to use all the money in your hand. For example, you might prefer gold to province at this point, but you've got $8, so what do you do? Or you prefer a $5 to a gold, etc. When you have +buy, then getting lots of money early is no problem cuz you can spend it all. So plaza has a strong advantage when +buy is unavailable. Saving your money now makes it much easier to consistently hit $8 later.
I think, your examples don't affect the +buy question. 8$ with need for gold? Play Plaza. 6$ with need for a good $5-card? Play Plaza. Both works with or without +Buy.
On the other side, the importance of Extrabuys lies in the end of the game; usually, you want to go green late, and Coin Tokens help you doing so; but you cant spend your big savings late without +Buy.
I think you're right that those two examples don't really help my argument, but I maintain that Plaza is better in the absence of +buy in the general case.
Plaza allows you to save your unspent money for later. When you have +buy, you're better able to spend all the money you have every turn, so
you're less likely to have unspent money. When you have +buy, you benefit less from saving your money for later. Therefore Plaza is especially useful when there is no +buy. I don't understand your objection to this part of things.
In a board without extra buys, your goal is to get to $8 quickly and consistently. Plaza helps considerably with consistency, though it is kind of revenue neutral so it's not necessarily that great speed-wise. Plaza is strong in engine-money hybrids lacking +buy and handy in more straight money strategies (probably more so in non-draw money strategies, e.g. Monument or Merchant Ship, where you usually get more terminals).
Now, Plaza is not particularly efficient at producing piles of coin tokens unless you can draw your whole deck. If you can draw your deck, then you draw and discard the same treasure repeatedly. Plaza is very strong in that case: once you've drawn your deck, it's a cheaper baker that gives +actions, and you (usually) need those +actions in order to draw your deck in the first place. Once you draw your deck, CSM is also strictly better than baker, but it doesn't draw or help cards that do draw (like a village does), so it's much harder to draw your deck when there are lots of CSMs in it. Plazas are superlative in this case.
When you can't draw your deck, Baker, CSM, Butcher, and especially MG are all better at producing big piles of coin tokens for a number of reasons. First and foremost, you don't need copper/treasure in hand in order to get a token with any of these. In addition, each of these other cards actually produces money, whereas Plaza transforms money in hand into tokens with no net gain. (CSM doesn't draw, so it's less clear cut in this respect, I grant you, but it does provide +buy which is necessary for a stockpiling strategy, as you point out.) This may be obviouss, but I have to add that big piles of coin tokens can be a trap. It's a lot harder to achieve than just putting a lot of treasure in your deck, so you need a good reason to go for a coin stockpile strategy.
I think looking at Plaza as a tool to create a huge stockpile of tokens is wrong in general. It can do that when you draw your whole deck, but that's not so common. Critically, boards lacking +buy discourage you from trying to draw your whole deck in the first place, leading to the larger point that
Plaza is not hurt by lack of plus buy; what is hurt is the engine that draws your deck, not the Plaza which provides payload for that engine. On the contrary, as argued above, Plaza is especially useful in the absence of +buy.
