In my opinion, the MK7/7.5 is only worth the upgrade if you want an improvement in perceived quality. The MK7 is considerably quieter and more refined in the cabin.
It's a far better made car than the MK5. Tighter, more uniform panel gaps, much sturdier interior with fewer cheap plastics that creak when push on them.
Driving dynamics are sharper than the MK5 too. Much sharper turn-in and good composure over bumps. Very easy to drive quickly.
Two areas that I hoped would be improved over the MK5, which haven't been, are tramlining and steering feel.
Think of the MK5 as a game changer compared to the MK4, but think of the MK7 as merely an evolution of a MK5 (albeit a good one) and you won't be too disappointed. But if you buy a MK7 thinking it's another game changer, you will be.