Hey, let's talk a little bit about cards--specifically when they serve multiple-purposes in a game.
My first exposure to the concept of "card as mutli-purpose game item" came when Star Wars CCG erupted on to store shelves in 1995. I was in complete thrall to the CCG demon in those days, and being a Star Wars nerd to begin with, no way was I going to miss that.
It was different in a lot of ways from most of the CCGs out there, several of which had contented themselves with trying to ape Magic: The Gathering as much as humanly possible. Star Wars dealt with battles happening at many locations, and introduced a 3-dimensional spatial element to the game--locations were "adjacent" to each other, yet you could travel between planets using starships--but what struck me the most was how each card in your deck served multiple purposes.
First off, cards were your life. Simply put, you took damage in the form of the loss of cards, often from the top of your deck. If you ever ran out of cards in your deck, you were dead, kaput, "one with the force", whatever you want to call it. Unlike other CCGs which had a minimum limit but you were free to play as many cards as you wanted, Star Wars CCG required exactly 60 cards in your deck. There was no need for dice, or score cards, as the cards kept track of the "score" for you, a very efficient use of in-game components with no muss and no fuss.
Each card of course served a game purpose, and came in all sorts of flavors, from characters like the good Admiral Ackbar above, to weapons, to ships, to planets, the list goes on and on. What's nifty about this is that each card in your deck served a *third* purpose, and that was in the form of the in-game 'currency' or 'mana pool'. You had a number of icons on the board of your color and you could "activate Force" equal to that number, which meant taking cards one by one from the top of your deck and putting them in a "Force Pile." This was how much you could 'spend' in one turn to bring out your cards. On Admiral Ackbar's card, the white square in the bottom left corner was his deploy cost, meaning that you had to take four cards from your Force Pile and placed them in a "Used Pile" that would be circulated at the end of your turn back to the bottom of your deck.
You could save your Force for future turns, often done when trying to lay a large beatdown at a key location, allowing you to bring multiple troops and characters in at once. However, any cards you drew had to also come from your Force Pile, there was no automatic end-of-turn draw. This meant you needed to balance how much Force you could spend every turn, how much you might need to save, and how many cards you wanted to draw.
Lastly, each card had a numeric value in the upper right hand portion of the card, called a "Destiny Number." Instead of using dice to resolve random elements such as blaster fire or certain characters trying to use the Force, you would draw a card from the top of your deck, reveal that upper right-hand number, and compare it to whatever you were trying to do (to hit people with weapons, high numbers were good; when trying to use the force, the lower the better.)
Being a CCG, this meant that you could in essence "stack the deck" by including lots of high-value numbers. The trick was that generally speaking the more directly useful a card was, the lower its value. Ackbar above is a solid character with pretty good stats and great piloting, so he gets a lower value. (They did throw this out of whack by printing two ultra-rare characters that were super powerful yet had a 6 for a destiny value, but we won't go into that right now.)
All of this made building decks for and actually playing Star Wars CCG a delicate dance. You wanted lots of powerful cards and characters but overdo it and your destiny draws would be too low to hit anyone with weapons. You only had 60 cards to work with so you had to be super-efficient with your card selections. And during a game, you were constantly having to balance the need for deploying, holding, and drawing cards. You see, when you drew cards into your hand they were no longer a part of your deck--meaning if you got too greedy, you would run yourself out of cards!
Once you had a card in your hand, there came the matter of when to use it, where, or if you should try to work it back into your deck somehow using certain cards.
The Destiny Values became a game of their own as many players became good enough to "track" a destiny value through their deck using card counting, so that when the time came they could use weapon fire and know for certain they would score a hit!
It all came down to the cards having multiple uses. This made the game great and in my mind's eye one of the best all-time CCGs that was ever printed.
During that time I wasn't aware that in the boardgaming world, the CDG had already been born with Herman's We the People. The true marriage of the multiple card usage hadn't been realized yet, but this was the game that seemed to take things down that path, affecting gaming forever. We The People spawned a legion of children that continued to enhance and refine this concept.
I think the biggest advancement on that front was the combination of event and ops on one card, seen first (I believe) in Hannibal: Rome vs Carthage, though the more knowledgable among you may be able to correct me on that.
Each card in your typical CDG has a value or "Ops", and these points enable you to take actions on your turn. This is combined with event text on the same card. When the event is not one of "yours"--ie, it doesn't have your icon or color and so you aren't allowed to play it as an event--the decision isn't very tough, you're going to play it for Operation points. However, when the card has some pretty sweet event text to help you out, you're often forced with a tough choice...play it for ops, or the event? Of course, Twilight Struggle took this a step further by allowing opponent's events to happen even when you play their cards for Ops, causing even more agonizing decisions about what to play, and when.
This is complicated further by what the Ops points allow you to do. In Hannibal you can use them to activate your generals, get reinforcments (with 3 Ops value card), naval travel (again, those valuable 3s), or put "Political Control" markers on the board. So even after you make the choice of how to play a card, then there's the matter of what to do with the resources a card gives you.
I think I like this so much because it gives me what I'm really looking for in a game--options. I like to feel as though there are many choices available to me, every turn. Even if some are obviously "better" than others, there's still the feeling that I have all of these tools at my disposal and it's up to me to figure out how to best use them.
This runs counter to some of the Euro design paradigm, where it always seems to be about constraint. Usually in the name of keeping a carefully balanced system purring, oftentimes Euro designs will continually restrict what you can do on a given turn. "Here, here's two actions, which can be used on three different things, and one of them will cost you both your actions." Either that, or the system conspires to reign you in at every turn lest you stagger outside the boundaries of the system.
There's a Euro that I enjoy that has both of these features, for good or ill. San Juan mirrors Star Wars CCG's efficiency in that it follows a very simple equation: Cards = Goods = Money. Cards in hand are buildings. They're also the currency with which buildings are bought and paid for. If you earn money, you earn them in the form of more cards. You can produce goods (yep, represented by cards) and when you sell them, you get...more cards.
It's still designed with a system that constantly feels as though it's restraining you. If you build something large, or eek out ahead, often you'll find yourself having to build back up your cards in hand, all the while the rest of the table catches up on your "advantageous" position. Of course, since the cards do vary wildly in power (seriously, Smithy versus Well? Prefecture versus Tower? Give me a break!) it is possible to "rock" the system just enough where you can break these restraints and pull away from the other players. Then again, by that time there are only a few turns left anyway, so it's not that big of a deal.
The evolution of the CDG seems to be continuing to load more information onto the cards themselves, to continue to increase their range of possible functions. Look at a card from 1960: The Making of the President:
There's the typical breakdown you expect to see from a CDG card--the Ops value (in this game, called "CP" or Campaign Points), the event text, and who it belongs to--in this case, the donkey icon shows it's a Kennedy card.
However, this system adds a balancing mechanism in that cards with lower CP grant you "Rest Cubes", essentially a chance to 'stuff the ballot' of the game's sole random mechanic in the form of drawing cubes from a bag to resolve certain game situations. Also, there are two other icons that pertain to other game functions--the "issues" icons to be used in debates, and a State value for the end of the game support checks in those states.
You don't want to trigger an opponent's event, and you want to hide it as the game allows you to stash a card at the end of every turn in your campaign book in preparation for the Debates. However, cards with your opponent's icons on them help *him* during the debates. So you're left wondering where to stash, what to stash, and even looking at your own cards and wondering whether it's better to use them for CP, for the Event, or try to load up to win the Debates later on.
Anyway, it's obvious that the CDG--and in turn, card as multi-faceted game item--is here to stay. Personally I hope to see a whole lot more of them.