i'm not sure, i've been using ps7 for a while now, and think i'm going to install 6 again as well. i have full 5.5 & 7, upgrade to 6. when i upgraded 5.5, it left both install versions on my machine (if i'd ever want to go back, i guess). 7 is cool and all, but i loke imageready v1.0 better, i haven't figured out to use the batch processing in IR7, i don't think it's available. otherwise, i could be wrong, but i have yet to notice a huge difference between 6 and 7. then again, i'm not an aged veteran of it.
so, my
says it's not really worth a substantial amount of money, especially if you have other things you can spend it on.