I feel like there's an article here, but every time I think about posting some kind of authoritative article, what I mostly want to do is get insight from the community on an issue (such as with my "payload first" post) so once again, I'm posting it as an open-ended subject.
Surplus
Cards in Dominion are costed according to their function. What if you buy a card and are not using some key part of its function? Surplus anything left at the end of a turn could indicate that you're overinvesting. Sometimes that's acceptable, but sometimes the surplus can be used as a guideline to identify bad play or bad buying decisions. So, at the end of a turn, what do you have left over?
Extra actions -- Don't overinvest in cards that generate +actions you don't need. You could be a Village Idiot.
Extra coin -- Don't overinvest in coin-generating you can't spend if there's no +buy.
Extra buys -- Don't overinvest in buys that you don't have the coin for.
Extra action cards -- Don't overinvest in terminals you can't play.
Extra value -- "Gain a card costing up to X" is a fuzzy category...it's frequently worth it to gain a card costing less than the maximum, but there could be some lost efficiency here.
Extra cards you couldn't draw -- All the cards left in your deck were an investment that didn't pay off this turn. If you can only draw half your deck, you've paid for cards that you can only use every other turn, making them fundamentally half as valuable.
Extra cards you could draw -- Overdrawing is a thing you want to do, but even then, it's possible to overdo it. If your deck is in hand and you can still draw more cards than you could possibly want for the whole rest of the game, you may be overinvested in draw (I hesitate to even suggest this, but I've done it.)
Underbuying -- Some cards are just terrible without the overpay. You generally don't pay $3 or $4 for a Masterpiece, or $2 for a Stonemason; doing so would be failing to use a key feature of the card. (Herald gets a pass. Buy all the $4 Heralds you want.)
Dominion is about efficiency, and if one player wastes resources and the other doesn't, the more efficient player is more likely to win.
So here's the question: What common overinvesting do you see when playing? Which ones would you consider mistakes, and when is it just a side-effect of wanting a unique function of a card that just happens to be giving you something else you don't need?
Here are some examples I see with particular cards:
Festival -- if you're not using the actions and/or +buy, you're paying $5 for Silver.
Minion for $2 -- I've seen players literally never get a new hand in a whole game. Facepalm.
Witch for draw -- if the curses are already gone, that's a $5 Moat. (Torturer, fine, I'll pay $5 for a Smithy.)
Wine Merchant -- if you never buy multiples, and you always leave $2 to get him back, that's a $5 Woodcutter.
Bank -- if ever a card needed +buy...
Highway -- is there +buy or gainers? If not, it's a bad Treasury, worth $4 according to conventional wisdom.
Cursed Village -- Used with terminal draw, it's a $2 Necropolis that hexes you. This is essentially another category: Any time you have a draw-to-X in hand and your hand is already >=X you've overinvested.
Scheme always topdecking itself -- Why did you buy it?
Ghost with deck in hand -- Oops. Exorcise something into an Imp right now or be sad.
Settlers with no Copper. Bustling Village with no Settlers. Either one with no discard pile or sifters -- You have paid for functionality you're not using. Maybe it's worth it, maybe it's not, but it's worth pondering if your plan could have been better.
Notice that I'm not listing bad cards here. I'm listing good cards misused by not taking advantage (or not being able to take advantage) of their natural synergy with other card categories.
Sometimes the overinvesting is subtle. I got into a long argument about Highway + University not being a synergy, and it hinges on this very issue: If you're not gaining $6/$7/$8 actions, University is overinvesting in surplus gain value. If you're not using the +2 actions, you're overinvesting in surplus actions. Highway (even without +buy) gains more Highways faster than University because of the addition of two stop cards (University/Potion) to the deck. With +buy it's not even close. And without +buy, Highway might not even be good. (But since many +buy cards are terminal, you might need that University after all!)
There are also plenty of examples where surplus just happens, such as City chains, Champion, King's Court -- lots of explosive engines accidentally generate gobs of +Actions that you don't need once they go off. KC often accidentally generates a bunch of +buys and other things you don't need, as well. But even then, the surplus could be a good indication of what to buy for next turn (if there is one!) Also, you sometimes generate surplus because you're battling to win the split on a key card, which will result in some inefficient turns after the pile empties but before you've bought the other pieces. But battling too hard over a split can also lead to suboptimal play, and a large surplus of anything helps expose this.
Thoughts?