Well, if you got constant 80 fps in your game, at such a high resolution, there's no reason whatsoever to upgrade your video card, IMHO!
But many of us are not so fortunate. I've been getting pretty poor framerate on the newest games from my Voodoo5 5500 AGP. Like an occasional 10fps stutter (though the average FP is usually higher than that). That's not playable! And I usually run my games at 1024x768 or 800x600. Sometimes I even had to drop color depth to 16bit, and still have the stutter. There'll be more games like these that will tax your video card in the future, not less. So, I've been wondering if it's time to upgrade. Though a GeForce 3 is absolutely out of the question!