Having spoken to restorers, the bass of the new is multiple times better. The mids are also better, but Henk uses the old ribbon only on the grands (which were the latest from Jason Bloom) and he does not see the need to replace them. For other models he said he will never go with the older ones. Also, he retains the crossover points as original just replacing the components, while the U.S. And UK restorer also change the points
Just to clarify I don't change the crossover points on any of the speakers, but I do adjust the top end circuit on the Duetta usually on site to what the owner wants to hear. They often gets used to the falling top end (high frequency drop-off caused by old stretched ribbons) the owner has ended up tuning the system to suit, so the speakers are set the the "standard" setting but end up sounding too bright, experienced this recently.