I'm a little bit late in this thread, anyway, being a G-70 owner and having tested the E-80 at FMM I can say that, compared to G-70, E-80 has a lot of new drum sounds, new guitars and basses, and the piano sound of G-70 (that was taken from Fantom-X) has been replaced with the new piano sound taken from RD700SX/SRX-11.
E-80 has also more MFXs available, so that you can apply multiple effects to styles, songs and realtime parts in the same time.
It has also a powerful amplification system, but, being a 61-keys, it doesn't have the wonderful keyboard of G-70.
I'm undecided about changing or not my G-70, because the new sounds and features of E-80 are amazing, but I'm afraid that I'll miss the touch and extension of G-70 keyboard.