I think it is all dependent on how much you use EQ 7 and how comfortable you are with computer programs.
I started with 5 and have now upgraded through 8. I did the upgrade when it first came out. I agree with PatriceJ - the interface is different and it took me quite awhile to get used to. In all honesty, EQ7 covered most of everything I really needed to do and as always there are many features that I never use. The one ability I love is I can easily manage the computers I have EQ loaded on unlike 7 (there is a tab in EQ8 where you can "deactivate" a computer).
I am a techie so play with EQ for almost everything I make so the upgrade was good for me.