How much have components/frames changed in the last few years?

I'm riding a beater rigid Kuwahara so anything is going to be a step up, and I've been looking at everything from a RockyMountain Trailhead (1000Cdn) to the Kona Kuna deluxe/Stumpjumper Comp. (1800ish).

One of the LBS's has a 03 and an 04 stumpy on sale for just under 1000. One of them is slightly used, some scratches but looks in good shape. The other is new but has V brakes (which is why no one is buying it). I am going to be pretty much just XC trail riding, and I'm not intentionally going out in terrible weather.

So how do the 03 and 04s compare to the 06-07-08 gear? Has derailers/frames/forks improved dramatically? Or are we talking grams?