It depends on the gaming experience and what else you do with the computer. There are always a lot of ''ifs' when coming to gaming and computers. Computers are evolving faster and faster. There is no way of determining at what point this or that is going to be ok, or good, and obsolete. I mean a p4 and 1 gig of pc3200 and an x700 can play Oblivion and most games nowadays. It just depends on the eye candy and special effects a person wants. It is my opinion that most gamers are computer enthusiasts, at least those who primarily play on PC's and want more than just to play a game, but want to 'max' out the settings.
I wouldn't make any assumptions, and upgrade when possible the best you can to stay on top of things.