It occurs to me that "Economy" is a concept in Dominion that gets mentioned frequently in the context of many discussions and articles on the wiki, but it doesn't have its own wiki page.
I don't think I have the expertise to write such an article, but I thought I might throw the idea out there for discussion, partly because there are so many different ways to build your economy, and especially for beginner/intermediate players, it might be interesting to point out some things about economy that are worth thinking about. I'm going to pose these in the form of questions rather than authoritative statements, because, again, I'm not necessarily an expert; I just suspect that these are issues worth discussing:
-- Economy vs. Mechanics?
When building an engine (or even a BM deck) you're doing two different things. Buying parts that create coin, or parts that do things that are NOT creating coin (drawing, cycling, sifting, upgrading, trashing, etc.)
The timing of exactly when to buy one or the other is surprisingly tricky. Buy too many actions without economy, and you end up with a lot of cycling or drawing and routinely getting $4. Buy too much money without actions, and now you're building a BM deck that makes $10 with one buy when what you really want is to stock up on power-$5s. That said, when is a +buy card worth overbuying worth opening with? I was scolded in another thread for suggesting opening with Herbalist if it was the only +buy rather than paying $10 for it later. I didn't think about the implications of what it would mean to draw it in the next three shuffles for single-buys with $3 and $4 and $5 when it could have been a Silver buying $4 and $5 and $6. One half-wasted turn later is better than three half-wasted turns now. This is a general economy principle that can be applied to many cards (Herbalist, Candlestick Maker, Squire, etc.) and belongs somewhere other than the discussion on these individual cards. I don't think the "opportunity cost" page is quite sufficient.
Multi-trashers introduce even more complexity. You should trash aggressively with Chapel; when do you buy the Silver you'll need to build back up? When do you open Chapel/Silver vs. Chapel/Action? I know it "depends on the kingdom" but some statistical economy guidelines that can give people an idea of what to expect on their next shuffle would be good. For example, it might be nice to have some probability charts of opening buys, or post-chapel second shuffles with a buy, that show the odds of making $4 vs. $5, of getting terminal collision, etc. Probability charts for dice and hits make visualizing Backgammon strategies easier; I see the charts when I'm pondering what to do with a roll. Something similar could be helpful here. I know the cards are all different, but odds for deck size vs. terminal collision and coin/draw samples for economy analysis would be handy.
Are there some solid numbers/simulations that can give some ballpark "feel" for whether it's better to buy Silver, or terminal +coin, or a terminal +buy/+coin, and on what shuffles?
-- Types of economy?
The canonical engine building strategy article on the wiki states that if your engine payload is treasure, then you might as well have just been buying money all along. I assume that even one small wrinkle, such as the availability of +buy, can make the difference between an engine board and a BM board. $16 and +buy, even without an attack or +victory token, may be worth building an engine for if you can do it fast enough.
But there are a huge number of ways to get coin, all of which have very different implications and statistical analysis possibilities. I'll list a few different economy approaches and invite further insight and discussion.
Big Money: Buying the largest treasure you can afford. Coppers buy Silvers, Silvers buy Golds, Golds buy Platinums. Even when engine-building this is sometimes the best way to build economy (maybe it's the only way!) But sometimes it's not the best way, especially when engine-building. Not every player thinks about this.
Special treasures: Most special treasures add economy in unusual ways. The value of a Venture is variable, but could be outstanding in the right deck. Treasure Trove increases economy, and I keep underestimating it, but it would take a deck-drawing engine with Goons-engine-like copper trashing reliability to be worth playing in anything other than BM/Slog. The special treasures all have their own articles, but they're usually for economy-building, which makes me wonder if there are some economy meta-principles worth enumerating.
Silver flooding: It's not just for Feodums anymore! Somewhere along the line, the experienced players and number crunchers figured out that flooding your deck with silver and a few key terminal actions can buy a whole bunch of Provinces AND be resistant to greening. Gold, Shmold. When is a silver economy better than Gold? Certain cards/events make it attractive (Jack, Trader, Delve) but this might need its own article, or at least something on the wiki pointing out that it's a thing.
Disappearing Money: There's an article about this on the wiki, which is good. Most players get the village/smithy draw engine idea right away. The disappearing money/draw-to-x engine, on the other hand, takes longer to sink in. Minion helps by demonstrating a one-card way to do it. But I've seen too many players buy up Festivals on boards with no draw and literally never use them for anything other than expensive Silver. A comparison of a deck-drawing engine with/without Festivals and showing how much treasure you can do without might be a good visual to explain when and why it's a good card, and perhaps that could be extended further into more general-case deck builds.
Cantrip Money: Sometimes it's amazing. Sometimes it isn't. It all depends on the likelihood that the one card you're going to draw is going to help. Peddler-BM isn't a thing. Getting a stack of free Peddlers with a bunch of +buy actions is awesome, but even then, it wants trashing and/or draw. How do you calculate the value of cantrip-money and what it means to a build in terms of the amount of Treasure you don't have to buy? Calculating average coin per card density with just money is easy. With cantrips, how do you calculate that? Maybe it becomes a draw-reliability calculation?
Terminal Money: The Tale of the Sad Conspirator. When is it worth buying multiple +$2 terminals instead of Silver, for example, when you have actions to burn (City chains, etc.) My guess is that it's worth it only when they do something else helpful, like attacking or trashing (or, in the case of Happy Conspirator, drawing.) How does that add to the economy discussion, particularly when deciding how many Silvers to buy early on when engine-building? How often do you want to buy Silvers early just to trash them later, or is that usually an indication that you didn't plan well enough?
-- How much?
Big Money aims to buy a Province a turn. Engines usually aim to buy at least two, though sometimes the point of an engine is to achieve greater reliability, particularly in the face of an attack card like Militia, and still get only one Province a turn. Slogs and rushes usually aim to achieve a reliable $5 or $4 a turn, depending on the Alt+VP available.
So what do you buy, and what does a build look like that gets the right amount of coin? In a reliable deck-drawing engine, counting to $16 is pretty straightforward, but building for a slog or rush is different, and BM buys far more money just to get the density up since it's not deck drawing. When do you stop building economy and start greening?
Maybe this is too broad a subject, but when players are evaluating a card and talking about how it helps or hurts economy, that's a very simple word with a lot of complex implications, and maybe it would be possible to take a look at that word on its own for a moment and offer some clarification and solid playing principles.
