Recently I've been migrate from a few months old Aura 6'' to H2O 6,8'' (I keep both devices, the 6'' exclusively for the road and, occasionally, for walk and trips) and I love the screen size of 6,8.
I read a lot of epubs but I need the bigger screen for pdf magazines. I think the 0.8'' is a huge improvement over the 6'', especially for reading pdf books, comics and magazines.
The 9+'' offers far better reading experience, but I thing is more expensive and lose the mobility...
In a few words:
Yeap! Is worth it!
If you have some time, take a look in the video below. Describes the differences of 6 and 6,8 of Kobo Aura series:
https://www.youtube.com/watch?v=2XKEyV5xAEk