I upgraded from 3, so there were more than enough changes to make it worthwhile. From 5 I think I remember seeing that the background saves and overall faster interface were new. Not sure what the speed difference from 5 to 6 is, but from 3 to 6 it was very noticeable.
Then there's one other thing that I use all the time but I don't know if most scrappers would even notice. You know how things in the layers palette have a box to the left that can be gray or colored? In CS6 you can change the box colors of everything you have selected at once. It's wonderful for altering templates when you want to mark what is part of a particular grouping. I used to have to change them one by one, and it was a pain!
One other thing to take into account is that Adobe has changed their upgrade policy. If you qualify for an educational discount it's a moot point, but for everyone else you'll only be able to get upgrade pricing if you have the most recent version. So you wouldn't be able to upgrade to CS7 unless you upgrade to CS6 before CS7 comes out. I think that change goes into effect in late 2012 or maybe Jan 1st 2013, but you'd have to check the Adobe site to be sure.