Is it worth buying a newer one for more money instead of keeping CS which I have recently acquired through an undisclosed means? How much better are they?
Keep in mind though, that while CS3 does have some great additions over CS2, that the new UI for CS3 is an acquired taste. I personally can't stand the single bar that was introduced in CS3.
CS2 is pretty standard for everyone, CS is fine too, CS3 is even better but it only has so little more additons from the previous version and its a whole lot more space reqiured for what it's worth. I have a CS2, though i could just stick with CS.