I think video cards have a better life span than we give them credit for. I've got a Radeon 9700 Pro that I probably paid a hefty amount for about three years ago. It's holding up just fine.
Video cards sometimes last as long as you still want to use them. What I meant about the card's lifespan was that newer games tend to shorten the card's lifespan. Also, the price drops that occur because newer cards are released. Thus you have a $400 card that has become a $100 card for your wife in a short period of time.
And there's no way the older generation of cards are handling the new games just fine. Doom 3, F.E.A.R., and a few others can really choke your system with the features turned on.
I just wish devs and cards makers would get on the same page. Instead, we have ATI and nVidia racing back and forth against each other while devs are struggling to implement some new feature in their game to take advantage of ATI/nVidia's card.