The extra VRAM is quite simply not of any use to most people these days. Few games currently take advantage of that much VRAM, and the system rarely does. Unless I REALLY knew I needed 256MB for some reason, I wouldn't even think about it. Are you planning on doing high-end gaming or running motion? If not, don't worry.
That said: $1000 MBP, and you're wondering whether to buy it or not?! Either it's stolen, there's something seriously wrong with it that is not covered by the warranty (or voided it--it got dropped or something), or the guy selling it is an idiot.
There's no way a fully functional MBP that's still under full warranty (and it's not old enough for the warranty to have expired "naturally" yet) is only worth $1000. Rember that if the warranty hasn't been voided by an accident, you can still buy another 2 years of AppleCare for $350 (or less, if you shop around).